How much life can I expect to get out of my Powermac?

I don't come here a lot so forgive me if this topic has already been covered.

I have 2002 G4 Quicksilver and I think I've gone about as far as I can with it, without a Pentium chip processor.

I am running Mac OS10.5.8 with a Dual 1.6 GHz PowerPC Processor. Since upgrading to 10.5.8, I'm not able to use my scanner or iPhoto and need to re-open in 10.4.11 for that. it's annoying, but I can live with it. the problem is, most software type stuff becomes problemmatic when I try to upgrade. I'd like to have a computer that doesn't rquire special knowledge in order to use it.

My question is, is there a powerMac 'box' (like a G5) that I could get and transfer my drives, cards etc that would use the pentium processor enabling me to keep going, or am I at the end of that road? I am happy with the mileage I've got out of my G4, and would understand if I cant go farther, but like I say, could I pick up a used G5 body that I could upgrade to the oint where it could keep going indefinitely? or at least for another 5 years (till one kid gets thru college)?

thanks!