I can't remember how many times I would be walking through a dungeon in Oblivion and an enemy dropped a weapon and I was all "Dood, that thing looks sick, lemme see what it does...... fortify speechcraft 15 points.... neat....". How about some good stats this time around, i.e. gauntlets that fortify strength 10 points and endurance 5 points or a robe that fortifies Intelligence by 10 points and Destruction by 15 points, overall just stuff that's useful, not a helm that boosts my mercantile and water walking! And while I'm at it, maybe have unique armor sets depending on skills like dual wielding, two handers, bows, etc just so every one of your characters isn't wearing either daedric or glass.
Useful is in the eye of the beholder
even thought those "beholders" may be quite few, but I shall take the challenge of finding a use for any item + enchantment combination anyone can think of upon myself! Starting with those you mentioned.
Weapon with Speechcraft = A bard may carry a dagger for protection but his main passion is the art of words and his dagger suits his needs perfectly.
Helm with Mercantile and Water-walking = A tradesman may have to travel great distances in Cyrodiil between towns and as a simple trader he has few combat skills to brag about, but with his helmet he can buy wares in the Imperial City at discount prices and travel with them outside of the city from the Talos Plaza District where he can start his route towards Bravil safely walking on the water where no monsters will assault him (can′t trust those imperial watchmen to keep the roads safe these days one can′t), so his helm both aids him in his bartering and allows him to have safe transportation monster free between certain points of interest.
But I do get what you mean, after all if you loot strong monsters in a cave why would you feel rewarded by getting items designed for those who would not partake in combat, there should be like 85% chance of good useful weapons dropping in dungeons (since ofc you′d expect most of the items to come from adventurers who failed) and the other 15% should be for the sake of immersion or just randomness if you like where the monsters may have gotten it from some poor chap who didn′t even venture there in the first place.