PPC is great for "legacy" software that can't run elegantly any other way. I run on my PPC:
The Grand 2 by Steinberg (I just have a a particular liking fo this piano set)
VE Pro 4 Server 32 hosting Kontakt 3, in turn hosting NI LX Piano through Guitar Rig 3 (you can't run GR 3 any other way without hogging the life out of an Intel machine (YMMV) and GR 4 does NOT load GR 3 sounds correctly).
Spectrasonics Trilogy often gets an airing on my PPC too. I have done this via Kore Player hardwired, and not tried this through VE Pro.
But yes, forget running anything that NEEDS K4 and up (eg Spitfire).
I have also used it as an external effects rack, running Altiverb etc. Or one could consider using it for Powercore, if you have it, to presever THAT particular piece of "legacyware". Whether or not plugs work via VE Pro is anybodies guess, but I have tested Powercore this way and the few plugs I tried DID work.
I have also run VI on the PPC too. It used to be my woodwind deck. But a little pointless now with the power of the newer Macs.
Don't sell that PPC. You will get £100 and then regret it immediately.
B