Right now, troop training in cities is basically a time based affair, and the occasional item put on the unit increases the time to train only based on the piece of equipment.  But what is training?  It's getting better, physically and mentally.   And all units have stats of strength, dex, intel, constitution, and charisma, right?  So, let's put those to work instead.

Make every item equippable have a minimum stat requirement.  Training of troops, or groups of troops, requires 1 turn per stat point raised.  When the troop is recruited from the general population, he has the basic stats: STR10, DEX10, CON5, INT10, CHA10.  Let's say I want to put him in leather with a pointy stick, which requires 13 STR for the stick, and 13 DEX for the armor.  It will take 6 turns to train this troop.  Training for groups, once the tech becomes available, should take the same time as training a single, since they're all working together as a unit to train (it also is what the principle benefit of getting that tech should be, not the ability to train troops together, but to actually train them together and produce time economies of scale).

Right now, there's 6 "action" stats, Accuracy (ACC), Dodge (DGE), Hitpoints (HP), Magic Resistance (MR), Attack (ATK), and Defense (DEF).  I leave moves (MVE), Combat Speed (SPD), and Sight (SGT) off this list, as they should be bumped separately, using spells or the experience level of the troop instead (eg, for every level, they get +2 HP, +1 SPD).

But these 6 stats could be tied to the 5 basic stats in a way that spending training time for your troops could impact the action stats.  STR could affect ACC and ATK (I know, we just fought to have these decoupled for combat, but for the purposes of training only, they could be linked).  DEX raises DGE and DEF.  CON raises HP (which it does now). INT raises MR.

Now, instead of having just barracks and war colleges for training and generically decreasing training time, you have barracks to increase STR, Gymnasiums to increase DEX, another building (call it a obstacle course) to increase CON, War colleges to increase INT, and War Temples to increase CHA (under this, CHA could rightly be changed to willpower, that personal magnetism that lets you both attract heroes as well as resist the mental assaults of others).

This way, if plate required a 20 dex to put on, and a sword required 18 strength, training that troop would take 18 turns.  Sending an unarmored peasant out into the world with a strength 12 club would require only 2 turns.  You could still have buildings (or more likely upgrades to buildings) that sped up the process (say, 0.75 turns per point instead of 1 turn per point), but now it's a much more logical and consistently applied process.

Winni