The op-amps in what? A number of people here have had success with upgrading op amps in DACs and the like.
One thing to watch out for is whether your choice of upgrade is compatible with the thing you are upgrading. A quick search on google of the item name+'op amp upgrade' or something should yield a few discussions on exactly what you are after.
Personally I am a believer in op amp upgrades; definitely something worth investigating if you have the time/money/will.