I have no idea why nobody (that I know of) has thought of this before. This is brilliant. I'd love to see the game go this route, where "accuracy" (or whatever) is just another property that magic weapons can have, and otherwise the notion of "+X" goes away to be replaced by more interesting properties.
Isn't it essentially 3E? You had to choose between +5 or +3 Holy. Sure, you could stack multiple properties, but the basic idea was still the same - you choose between what special abilities your weapons have.
The +X is pretty boring. But the advantage is that it keeps players motivated to search for new magical stuff. Maybe the "wonder" of finding a +4 weapon after you own a +3 weapon is weak, but if you have a Flaming Longsword, are you really more interested in a Longsword of Frost?
So, you might find a new, cool magical item - and throw it away. Uniqueness and specialness of finding something new is gone.
If you don't throw it away, isn't it very likely that you end up lumping around 10+ different magical weapons that you all liked and keep around for "optimization" purposes? That was 3E had, too. Golfbag Syndrom - usually you might use your +2 Silver Holy Evil Outsider Bane Battleaxe, but when dealing with Golems, you put out that +1 Construct and Undead Bane Admantite Battleaxe that you put next to your +1 Cold Iron Evil Outsider and Dragonbane Throwing Axe.
Again, magical items just are a common tool.
A +x weapon clearly becomes obsolete and can be sold (3E) or disenchanted (4E) to get something better. If you really loved the Flaming property your weapon had, you could acquire (build, buy, search) another one at a higher plus.
In the end, keeping around plusses or not, the real "flavor" problem is that magical items are common and that you are forced into choices whether to keep them or discard them.
The only real compensation is that you never find more than one item of a specific type, and it grows with you, gaining new special abilities. In that case, you probably don't need +x weapons.
