I haven't changed the ELs, so yes, the wealth of the characters has kept their strength in check to some degree. However, everyone in my group also plays in another campaign with a different DM that is really high-powered. (My wizard in that campaign has a greater metamagic rod of quicken and one of empower, a constelation of ioun stones around his head, and more staves than he can carry, at level 12). It's like culture shock for them to be suddenly "underpowered". I'm afraid some characters are loosing interest.
So, I think I'll take Walter's suggestion and work in some more specific magic items as treasure. If that makes them world-beaters, I'll just have to make a tougher world ;)