BMedina,
We didn't have to reverse engineer SoundJam's visuals API -- it was a published format. We chose to support it to save the visual plugin authors the pain of having to rewrite their applications for a whole new API.
As for a performance hit, our testing shows that it's just as good as any other player. Of course, visuals will be much smoother when the visuals window is in the forground and getting more CPU time from the Mac OS. (Bring on X already!) But then, why would you want visuals in the background? They're for show, right?
Of course, encoding, the equalizer, etc. can all slow down the visuals as they all require CPU time as well.
Since this is our first "round" of visuals work -- we added it after much hesitation -- we'll continue to fine tune and improve it in the future.
-Cabel / Panic