Well, I just finished maxing out my old G4 400 PCI to the hilt (O/Ced to 450, max RAM, ATA/100 card, 120GB 7200rpm HD, etc.), so I'd say I'm good for at least another year. Long enough to wait out and see the direction Apple chooses to take with the PowerMac's processor.
Booting into OS 9 has saved me on several occassions so I'm grateful to still have it. I think it's good that they're forcing OS X booting only on new machines; I just hope they're prepared to face the problems that are going to crop up.