Well having the PowerPC architecture may limit you when it comes to compatibility if you are a software junkie. If you like working with the same software/version and don't really mind not having the newest thing you should be quite content with it.
Apple should be updating the Mac Pro sometime soon though. I think the processors are still Xeon 5400 series, which is a full generation behind current Intel processors if I'm not mistaken.
Basically, IMO, if you have the cash, wait for an updated Mac Pro. If you don't, a G5 spec'd out well would be good for most DAW work.