sambrookjm: How many items do you actually use, though? Serious question here, as I don't really find myself using any charges from any items once I get my Archmage up and running.
Here's how it has worked for me in the classic versions, in terms of things that were useful and not just "because they're there, so I might as well try to find a use for it":
BT1: I tend to use breath attacks all the time. Other spells in items aren't particularly useful. (Remember: The original didn't have those nice Wizard offensive spells, so MIBL (only 10-40 damage) was the strongest general purpose attack spell in the game.)
BT2: Cold Horn early in the game, before my spellcasters learn attack spells. Otherwise, it really is only in the Grey Crypt that I use item charges; Masterwands are good in the DOS version, while Dragonwands and Flame Horns are good in the Apple 2gs version. (In the DOS version, Dragonwands and Flame Horns, for whatever reason, are rather weak; in the Apple 2gs version, the Masterwand (and other spellcasting items) will not work in the Grey Crypt. By the way, in the DOS version, the Grey Crypt's anti-magic will actually cause ranged physical attacks from monsters to fizzle (the enemy throws a spear at you but it fizzles!).)
BT3: Useful after getting the Chronomancer class, as characters in this class lose their old spells and need to gain a couple levels to get new spells that are useful. Otherwise, it's really just Deathhorns (breath attack that critically hits a group; useful in Malefia but not necessary before then) and items with the Harmonic Gem effect (restores all the user's SP; Harmonic Gems are ludicrously common in the 8-bit versions). Due to limited inventory space, if an item isn't as good as a Harmonic Gem, it gets discarded. I note that BT3 does not have Garth's, so no recharging in classic versions, but there are ways to duplicate items in such versions.
To be honest, I am far more inclined to use item charges in games where it's possible to recharge such items, and the removal of this ability is one of the remaster changes I disagree with. (I actually think they should add this capability to BT3, for a cost.) It's bad enough that there aren't enough uses for money later on, anyway.
sambrookjm: If you want to stop the cheese factor, make the price of the item proportional to how many charges you've used. Item is fully charged? You get the full 50% back. Item is at 10 charges out of 50? You get 20% of the full sale price, or 10% gold. It has 1 charge out of 50? Enjoy getting 1% of the price you'll be buying it back at!
This is how Baldur's Gate and its sequel handle this.