PCI-e is all good, but i wont be changing for a very long time. VIA came out with a intel chipset thingy that is AGP/PCI-e compatable ( Two slots for each ) and is also DDR1 and 2 compatable. Check on there site for details. Problem is, its intel only stuff.
Only upgrade for what you need now. Otherwise, stick with what you have intil it becomes too unpractical to keep. Sooner or later, prices drop ^_^