Its fun to upgrade the old Macs but your 9500 isn't going to be as quick as a Quicksilver no matter what you do to it. If you watch ebay you should be able to find a pretty high end Quicksilver for $150 or less including shipping; a local one could be even cheaper. The Quicksilver's got a G4 processor, faster RAM (though I think in the case of the 9500 surprisingly they both can take the same max amount of RAM), AGP graphics, gigabit ethernet, USB, firewire, Airport (possibly), and ATA drives (not always a plus over the 9500's SCSI but cheaper in most cases). But it does have fewer PCI slots, no ADB, no SCSI or serial ports without a PCI card, and while G4s are cheap now your 9500 will run OS X and if you don't feel the need to upgrade it further, additional cost to you is nothing.

I had a mini "conquest" last night and picked up a few Macs. While I was more interested in the clone and 8500 with G3 upgrades in them that I got for $10 each, I paid the same amount for two 400 MHz G4 AGP Graphics. But, that doesn't mean I was not thinking about all the upgrades I could do to the 8500 on the drive home. And strange how I consider 4 computers a small haul.