I've only been kayaking for 2 years so take my info for what it's worth, but I found myself in your position at the beginning of the season so I figured I would share my input. I started with a dagger centrifuge the year before and it was great for learning, but I knew if I wanted to learn more advanced tricks it was outdated. I could do spins in my dagger and that's about it, but now I can do 2 ended cartwheels, wave wheels, clean spins, stern quirts, and the occasional loop though I haven't managed to land back on the wave yet. I picked up a 2011 medium rockstar for about $500 used and I think it was totally worth it (I'm 5'10" and around 150#). I wondered if I was going to be able to progress down river with it too and it turns out I did. I mainly only ran shoshone the year before; but this season I ran slaughterhouse 3x, pine creek 2x, numbers once, dowd chute 2x, bogan canyon (marble to redstone on the crystal), and barrel springs.
I haven't paddled any other play boats so I can't really speak to them but from what I have seen from the ton of time I have spent at the wave is that the jitsu and jed seem to be great boats as well.