The EFI32 in the '06 can be a problem though, as it's already limiting users for graphics cards (GTX285 won't work). Once OS X goes 64bit Kernel only, then those systems won't be able to upgrade the OS any longer either, and that's not going to be far off. Maybe as early as 10.7, as Apple doesn't like to carry interim products for long.
They're not likely to issue an EFI update to 64 bit either, as it will prevent the sales of new machines. But that's all the system actually needs, as the CPUs are 64 bit capable, and why the work-around for 64bit Windows will function.
If the OP doesn't need to have the latest and greatest graphics card, and can live with SL (assuming 10.7 won't work), then keep the system. Otherwise, it's time to think about upgrading. The '08's were the first systems to get EFI64, btw, so a used system may be a possiblility.