I reckon the 9200 is not an unreasonable investment. Unless you intend to eventually replace the Smurf with a late G5 or a Mac Pro, you can still put it to good use as a second card in anything up to an early 05 G5.
I bought a 9200 for the exact reason you mention. And I'm not one to spend more money than needed (cheap) but I planned on using the PCI 9200 in as many future machines as possible. The 9200 is currently in the GF's B&W and my G4 has a 32MB original Radeon Mac Edition running my second monitor. I never owned the 7000 version of the card but all the reviews I read gave the original Radeon 32MB card a better rating than the later 7000 series 32MB Radeon.
I could swap the 32MB card with the 9200 and she probably wouldn't even notice but I have the OEM 32MB AGP card in my Quicksilver and adding a 128MB PCI card for the second monitor seemed kinda backwards. I do plan on upgrading the AGP card to a 9800 Pro someday (when they get cheaper), then I'll put the PCI 9200 in the G4 then but it serves a better purpose in the B&W right now.
I honestly don't see much difference in my 32MB card and the 128MB card, but I have to admit I haven't really used the B&W with the 9200 card a lot so my comparison is pretty limited. I had the Mac Edition 32MB card in my last B&W (OS 10.3) and it worked well. No complaints at all.