Snow Leopard is going to be uber cheap, so there's not really any reason to not pick it up -- if you make good, regular use of your Mac, odds are that you'll also make enough use of a copy to justify the value. But even if you're not taking the $30 plunge, Macenstein has the most important part of the OS upgrade covered: the wallpaper. Just like the OS itself, Snow Leopard's wallpaper is only an incremental update from the current version (Macenstein says it looks "faster," and we can see what he means), but just in case you want to at least make your old G5's look like they're all upgraded, just "Set as Desktop Background" and there you go.
Rumors that the wallpaper will actually make your computer faster (or give you back that 6GB of hard drive space that the actual upgrade will give you) are unfounded, and probably shouldn't be trusted. But then again, you never know.