+1 weapons are fine. They are simple, but not every magic items needs to be complicated. The "interestingness" of magic items is based at least as much on their rarity as the complexity. If a character has 15 magic items, each with a contingent power and a 3-paragraph history, the player won't think: "Oh, what fascinating magic items." He'll think: "How do I simplify this bookkeeping nightmare?"
The problem is +5 weapons. If the math curve of 5e is shallower (a good thing, IMO), then high plus items will have a larger relative effect. In effect, WotC needs to push the interesting effects "down market." If a +3 weapon is an extraordinarily powerful magic item (say, a reasonable choice for an 19th level fighter), then 3e's system of magic weapons ranging from +1 to an effective +10 is entirely unsuitable for a shallow power curve.
Instead, I think we should have a level system for magic items, not unlike 4e's, but where the higher plus items are given more credit for their math-altering effects. For that matter, I see no reason a +1 sword should be a level 1 item. +1 to hit and damage is a pretty decent effect. Other effects could be added on to increase the level of the magic item, but without 4e's unusual, item-proliferating restriction of "one effect per item."
Naturally, I wouldn't want to see expected wealth levels or expected numbers of magic items, but it would certainly be helpful to have a chart that told me how wealth X in magic items affects the power level of PCs. In other words, if I give each of my 7th level characters 4 level 9 items, does that mean they should be able to take on a module for 10th level characters?
-KS