After all these hardware discussions I've come to the conclusion that the only major upgrade possible for a Sketchup user that will have any impact is themselves... meaning re-training themselves to work smarter within the limitations of the current system.
I will say that it is not a particularly compelling POV to pro users who can move onto "greener pastures" with multi-core, 64-bit, etc. type programs out there... I have the sense that alot of that is marketing hype, but the problem with marketing hype is it tends to work.
For what it's worth I can use Sketchup well at very high poly-counts without any real issues -- but I also dedicate alot of my time to "upgrading" myself.
Best,
Jason.