If it works, keep it.
I've gone through hell trying to upgrade stuff that actually didn't need upgrading.
Your G5 is a fab computer that does everything the Intel macs can (apart from boot Windows, and if you've been happy with the G5 so far, trust me, you don't *really* need to boot windows.).
I have a friend who brought the intel macs while keeping his G5, and he has been *disappointed* as the intel macs are *slower*. (cos not all his software is yet ported, and much has to run under emulation)
As well, if you keep your G5 another year, the price will only drop about $200 or so, while in a years time, you'll be able to buy the latest greatest intel macs, (or buy a second hand 2006 intel mac for nearly half the current selling price.)
In summary, if you have no mac, yes buy the intel, they're fab. If you have a modern current model G5 that is working well for you, it's also fab, and there's no pressing need to splash out yet more money.
..RedTomato..