What version of OSX is on your QS2002?
I have noticed on my older Macs that the latest Quicktime and ITunes run a bit slower than they used to back a few versions ago. That is probably part of what you are seeing.
I would suggest though running Onyx or MainMenu and do some maintenance and that might help the machine run a bit faster also.
I would not put that much into a G4 machine because even after your $800 it will quite a bit slower than even the first run of Intel Macs. If I was going to spend that much, I would save a bit longer and purchase a newer Intel Mac. The iMac would do quite well.
I have a Quicksilver 733 with 10.4.11 and have not upgraded iTunes the last few times as I was afraid of what you are running into on your machine.
I have a fully decked out G4 DA with a 1.8Ghz G4, ATI Radeon 9800 Pro, 1.5GB PC133 RAM (The RAM helps a LOT!) and USB 2.0. It's nice but my single CPU G5 even is way faster at most tasks leave alone any Intel Mac. I did it just to mod a Mac as I am a PC builder by profession and thought it would be fun, but it did cost me a lot. Don't get me wrong, it's way faster than it was but still for the $$$ no where near a modern Mac in performance.