Sounds quite good; I've never really seen the logic in Aerie suddenly gaining monstrous strength from touching CFaeyr, a hammer which, were it not enchanted, she wouldn't even be able to lift. It opens the door to all kinds of abuse, like my Cleric/Mage starting BG1 and using STR as his dump stat to raise all his others to 18--knowing that I could survive until getting the Gauntlets of Ogre Power, and then again in BG2 until I bought a Girdle. Softening the items in this way is more realistic.
My issue is, it seems inconsistent to do this for items and not for potions. Why should a Potion of Hill Giant Strength be far more potent (for weak people) than the Crom Faeyr? Then again, this inconsistency might very well make many potions useful again: If Keldorn is your Tank, Potions of Agility will still be useful, even after he's got the Gauntlets of Dexterity. This is definitely a good, balanced idea, and I'll be incorporatiing it into any mods that I make--for items, at least. I'm as yet undecided on what to do with potions.
More importantly, what happens when +stat items stack? If your Half-Orc (STR 19) Cleric takes the Evil path in the Test of Wrath (STR +2), equips his Holy Symbol (Str+1), and then Crom Faeyr (STR +4), would that not set his STR to 26, looping around to 0 and killing him instantly?