You will gain immediate benefit from Leopard as it will be more G5 centric than Tiger is. It is NOT useless at all. 10.5 is not for Intel only Much. It's all about the 64-bit you have. Just because it's single core doesn't mean you are out. It just means you are less in on the multi tasking front. You're cool with Leopard and you'll feel the difference right away.😎
Yeah, Leopard would be just as useful an upgrade (or not) as Tiger, for anyone. There's nothing multi-core-centric about it as far as I've ever heard. As far as anything Intel-focussed goes, I think the hope is that Leopard on x86 will finally be equal to the PPC version. (It's not for no reason that all of the 10.4.x Intel updates have been massively larger than the PPC updates.)
It'll be going on my 32-bit PowerBook G4, my 32-bit dual core Intel iMac, my 64-bit dual processor G5, and hopefully a dual core 64-bit MBP that I will buy after the release.
Leopard will be equally good for PPC and Intel, 32-bit and 64-bit.