The reason I'd care is in that word "properly" in your first sentence: the system bus IS faster than PCI (and in ideal conditions, faster than 66MHz PCI, too) so if we can get a little more, we get a little more. The fact that it isn't as fast as proper 66MHz PCI would be doesn't diminish the fact that it (would be / is) faster than it was before.
For example, I've got a Voodoo2 SLI setup here; I note that the Voodoo2 chipset can utilize AGP1x as 66MHz PCI, so it's likely that my Voodoo2 cards will work on a 66MHz PCI bus. It might be fun to run them at that speed, if they'll take it, just to see what performance increase I can see, if any.
It's a fun thing, like nearly all vintage computing is. It's highly unlikely that the PCI overclock, if it worked, would somehow save an old 9500 from needing to be replaced, for example. It's just for the hack value, and perhaps the added speed would make the experience a little more enjoyable.
For example, I've got a Voodoo2 SLI setup here; I note that the Voodoo2 chipset can utilize AGP1x as 66MHz PCI, so it's likely that my Voodoo2 cards will work on a 66MHz PCI bus. It might be fun to run them at that speed, if they'll take it, just to see what performance increase I can see, if any.
It's a fun thing, like nearly all vintage computing is. It's highly unlikely that the PCI overclock, if it worked, would somehow save an old 9500 from needing to be replaced, for example. It's just for the hack value, and perhaps the added speed would make the experience a little more enjoyable.