I dont know if ideas like these are already given but I think that something in those lines can improve the situation with ranged weapons in the game. Before I begin I wish to apologize for my bad english - it is not my native language.

The idea is simple: for ranged weapons to be a meaningful option in combat, they have to be strong enough in different phases of the game (beginning, midgame, endgame). That obviously can be accomplished just by giving them a higher attack rating and several different versions of ranged weapons for defeating higher defense ratings in midgame and endgame.
The obvious problem with this simple solution is that ranged weapons can become overpowered so they have to be balanced in some way. I think that it is better for them to stay relatively powerful (as opposed to nerfing their power) but to limit the number of uses per combat. This can be accomplished by introducing the ammo (or "charges" so to limit the number of possible ranged attacks per combat). That way ranged weapons will have good use in combat but the player have to decide what target he should engage (is it worthed waisting one ammo point on that?), should he spare some ammo points if combat is too long etc. Melee-units will have advantage of not being limited in that way.
Something in that direction is the initiative penalty already in the game (reduces the frequency of uses of ranged weapons in combat), but I think that the ammo factor is better solution (of course that should be balanced against duration of typical combats so to be really limiting factor). It was used in Master of Magic (and many other games with tactical combat) and I think that balanced ranged combat nice: they are powerful but that power is limited by number of uses per specific combat.
Of course this creates another problem - what ranged weapon unit will do when it uses up all the ammo? One solution is to give a possibility for a unit to switch weapons (if it is equipped whit ranged weapon to have possibility of additional "light" melee weapon: one handed like knife, short sword or some small axe) or every time when the unit is engaged in melee (or when all the ammo is used up) it automaticaly "switched" to this weapon. The second solution is to give every ranged weapon base melee form of attack which not use the ammo and have limited attack so when the unit is used up all of the ammo it still have some very limited military power. Or every ranged weapon to have base melee attack combined with additional abilities that have number of uses (charges or ammo) and are ranged so when ranged options are exhausted or unit is engaged in melee it will use the base (melee) attack.
I think that probably the last option can be easily used in current engine (but I might be wrong off course).
Off course that will give some possibilities for new spells like "steal ammo" (reduce ammo of the ranged unit) or "give ammo" (give additional ammo to ranged unit).

Ranged combat can be additionally "spiced" by giving more and different ranged weapons with different "special options" or form of attacks (maybe something like this is already proposed somewhere). Off course the special form of attack can be tied not to weapons but to "traits" given to archer-units.
My idea is to give several different non-magical ranged weapons so in designing a ranged unit to have additional options:

1. a bow "line" - piercing damage (like now), "point blank shot" (or "aimed shot") ability - used in up to 2 or 3 battle squares and ignoring up to 50% of target defense and +10 to hit; "rain of arrows" ability - hit area of 3 x 3 squares for 3/4 of normal damage and uses 3 points of ammo.

2. a sling "line" (sling, staff sling) - basic weapons doing small blunt damage, with ability to replenish ammo.

3. a crossbow "line" - powerful blunt or piercing damage, ignore up to 75% of target defense, huge initiative penalty (with some form of early black powder weapon on top of the line, which will do blunt and fire damage)

This is just one possible list (the numbers are subject to balance):

1.
[ranged weapon:] sling (for trowing stones)
[initiative:] +3
[type of attack:/value:] blunt / 2
[ammo:] 16
[melee form of attack:] blunt / 1
[abilities:]
1. gather stones - lose one "turn" (action) and replenish 4 ammo points (not above maximum)
2. rain of stones - distance up to 3 squares - hit area of 2 by 2 squares for 3 blunt attack, spend 6 points of ammo, cooldown 4
[tech level:] start of the game

2.
[ranged weapon:] staff sling (for trowing stones
[initiative:] +1
[type of attack:/value:] blunt / 4
[ammo:] 14
[melee form of attack:] blunt / 3
[abilities:]
1. gather stones - lose one "turn" (action) and replenish 4 ammo points (not above maximum)
[tech level:] early in the game

3.
[ranged weapon:] shortbow
[initiative:] +1
[type of attack:/value:] pierce / 5
[ammo:] 14
[melee form of attack:] slash / 2
[abilities:]
1. aimed shot - distance 2 squares (of tactical map) - ignore 10% of target defenses, +10 to hit, cooldown 3
2. double shot - distance up to 4 squares - 2 attacks, spend two points of ammo, cooldown 4
[tech level:] early in the game

4.
[melee weapon:] javelin (one hand) ammo (for trowing) 4
[initiative:] +2
[melee form of attack:] pierce / 8
[abilities:]
trow javelin: pierce 12, range 3, cooldown 2
crippling trow: pierce 8, -6 to initiative and -20% of defense of target for 2 "rounds", range 2, cooldown 4
[tech level:] early in the game

5.
[melee weapon:] trowing axe (one hand) ammo for trowing 6
[initiative:] +3
[melee form of attack:] slash / 6
[abilities:]
trow axe: slash 8, range 3
double trow: slash 14, range 2, cooldown 3, spend two ammo points
[tech level:] early in the game

6.
[ranged weapon:] yew bow
[initiative:] 0
[type of attack:/value:] pierce / 12
[ammo:] 12
[melee form of attack:] slash / 4
[abilities:]
1. aimed shot - distance 2 squares (of tactical map) - ignore 25% of target defenses, cooldown 2
2. barrage - distance up to 3 squares, hit area of 3 x 3 squares for 8 pierce damage with -10 to hit, spend 3 points of ammo, cooldown 4
3. flame arrow - distance up to 4 squares, 6 pierce + 6 fire damage, 1 point of ammo, cooldown 6.
[tech level:] early in the game

7.
[ranged weapon:] yew longbow
[initiative:] -3
[type of attack:/value:] pierce / 20
[ammo:] 9
[melee form of attack:] slash / 6
[abilities:]
1. aimed shot - distance 2 squares (of tactical map) - ignore 40% of target defences, +10 to hit, cooldown 2
2. barrage - distance up to 4 squares, hit area of 3 x 3 squares for 12 pierce damage with -10 to hit, spend 3 points of ammo, cooldown 4
3. flame arrow - distance up to 6 squares, 8 pierce + 12 fire damage, 1 point of ammo, cooldown 6.
4. bodkin arrow - distance up to 3 squares, 16 blunt damage, ignore 50% of target defense, cooldown 4.
5. howling arrow - only usable against mounted troops or heroes, distance up to 4 squares, 16 piercing damage, -25% to target defense, -25% to target initiative for two "turns"
[tech level:] midgame
[special:] can not be equipped by mounted units or heroes

8.
[ranged weapon:] composite bow
[initiative:] +1
[type of attack:/value:] pierce / 16
[ammo:] 12
[melee form of attack:] slash / 6
[abilities:]
1. aimed shot - distance 2 squares (of tactical map) - ignore 25% of target defenses, +10 to hit, cooldown 2
2. double shot - distance up to 2 squares - 2 consecutive attacks for 12 pierce, spend to points of ammo, cooldown 4
3. poisoned arrow - distance up to 3 squares, 12 poison damage for 6 turns, 1 point of ammo, cooldown 6
[tech level:] midgame

9.
[ranged weapon:] crossbow
[initiative:] -4
[type of attack:/value:] pierce/ 12, ignore 50% of target defense
[ammo:] 14
[melee form of attack:] blunt / 6
[abilities:]
1. careful shot - distance 2 squares (of tactical map) - ignore 100% of target defenses, cooldown 2
2. barrage - distance up to 3 squares, hit area of 2 x 2 squares for 8 blunt damage, spend 4 points of ammo, cooldown 6
3. ball shot (using stone ball) - distance up to 3 squares, 15 blunt damage, cool down 3.
[tech level:] midgame

10.
[ranged weapon:] steel crossbow
[initiative:] -12
[type of attack:/value:] pierce / 30, ignore 60% of target defense
[ammo:] 10
[melee form of attack:] blunt / 12
[abilities:]
1. devastating shot - distance 2 squares (of tactical map) - ignore 100% of target defences, 40 blunt damage, cooldown 4
2. preparation - +20 initiative for two "rounds", cooldown 8
3. pavise shield - cant move, + 20 defense from all missile attacks (or +25 to dodge only from missile attacks)
4. ball shot (using stone ball) - distance up to 4 squares, 40 blunt damage, cool down 3.
[tech level:] late midgame to lategame

11.
[ranged weapon:] thunderstick
[initiative:] -16
[type of attack:/value:] blunt / 30 + fire / 30, ignore 50% of target defense
[ammo:] 8
[melee form of attack:] blunt / 20
[abilities:]
1. devastating salvo - distance up to 3 squares (of tactical map) hit to consecutive squares, -10 to hit, cooldown 6q two points of ammo, +50% damage.
2. prepared position - cant move, +20 defence form all attacks, +2 counter attacks.
3. shiper shot - distance up to 4 squares, +25 to hit, ignore 100% of target defence, cooldown 4.
[tech level:] lategame