As far as I know, chests won't produce any better loot by waiting for higher levels - there's been some discussion on these forums about this topic before, but you're welcome to try to prove it wrong.
Loot is random though, and you can benefit greatly by (quick) saving before you open a chest or turn in a quest. If the loot isn't what you want, reload and try again - but note that you won't get much better than the 'average' for the reward. For example, if if you find a reward that gives +2 or +3 level charms, then you're not going to get a +5 level charm out of it, no matter how many times you try. But you might get a +2/+3 charm more suitable to your current needs...
I've heard that with chests, once you get too close, loot becomes fixed (even after reloading). I can't confirm this though, let alone tell you how close is 'too close'.
