Got some ideas for both champion items and standard soldier items, but I'll do the champions first.
IMO running around finding and buying items for champions is one of the most enjoyable parts of the game. When I play, this is always the part I like doing the most. That said, there's some ways to improve it:
1. Items at sovereign creation time are a waste right now. You spend points for items that can be replaced easily, in some cases simply by visiting the item shop on turn 1. Those points are basically lost, when you could have started with better stats, spellbooks, or abilities instead.
Instead of spending points on items at creation, give every sovereign a budget (say 100g) and a list of items to buy. Don't take it away from attribute points.
2. More variety in the stats on items. For a strong spellcasting sovereign, there is a much smaller selection of useful stuff. Where's the staff that boosts INT, or the robe that provides no defense but adds mana regen? Hell, it's a magical world, why can't I buy a ring that adds charisma?
It doesn't work so well for STR and DEX, as those two just modify attack and defense (stats which are already on items). But there's no stat to modify spell power or mana regen aside from INT and WIS, so those should be allowed on items, along with CHA and CON. That would dramatically increase the variety in items available.
3. Abilities on items. Amulets that add +2 whatever are fine and all, but what about one that provides a 25% chance to negate any incoming attack spell? How about an enchanted bow that shoots ice arrows (which have a chance to apply the snare that the attack water spell does, whose name I forget). Or a Mace so big that attacks chain to adjacent squares? How about a Holy Sword that boosts morale on my side of the field and grants me a once per combat unit heal?
Yes, some of this stuff would be really powerful. But there's nothing really wrong with that, interesting abiltiies on items make finding items and tactical combat both more interesting.
This idea also applies to standard units. When I get the ability to use horses, why not give me a more expensive option to use trained horses that add the Charge ability to the unit? Or when I can make shields AND have the enchanted item magic tech, allow me to use both metal and crystal to make enchanted shields that deflect ranged attacks?
Soldier customization would be more fun with more options, particularly a way to make very expensive special soldiers like this that have abilities. Same as with champion items, abilities make TC more fun, and it also gives me a way to differentiate between "peasants with maces" and the "Deathwatch Guard" (who are peasants with enchanted maces and black obsidian fire immune dreadplate).
To me it seems like some of the systems in place right now aren't being used as effectively as they could be, and I think this would really help improve a lot of areas of the game at once. Besides, who doesn't want a Sovereign using a Staff of the Titans and Infernal Robes, flanked by elite guards who can intimidate mere peasants just by the sight of them and cost a small fortune to build?