For an 18 team league your team is, and I don't throw this word around too easily, *excellent*. You have 4 great great starters (assuming brett myers and dontrelle willis keep it up, and they show no signs of slowing down), and very few holes on offense.
The one thing I would say that jumps out at me is Mike Piazza. He has gotten old quickly, and will kill your BA if you continue to start him. But then again, there really aren't many options at catcher, so I doubt you can get an upgrade. Honestly, I would keep your team intact unless you get some offers to upgrade at catcher or 2nd base.
Check out my team: http://www.fantasybaseballcafe.com/forums/viewtopic.php?t=126874