Actually I'd disagree.
I'm sure many folks who went from a 60/5400 drive to a 100/7200 noticed a severe difference. If you ever upgraded a P-M from say 1.6 to 2.26 you'd notice that too, unless perhaps you don't stress your system to begin with very much. Then I'll grant you that you might notice it less. GPU upgrades? How about the 6800 to the 7800? No difference? Again perhaps if you aren't maxing the 6800 there wouldn't be, but if you run Oblivion I'd bet you'd notice the difference in those two.
Again some people work their machines harder than others. I run macros in Excel where I can literally walk away from the machine for 5-10 minutes and come back. Games I run at 1920x1200 whenever that's an option, both externally as well as internally. So yes I expect to see a marked change going to the G80 if that's a possible upgrade route (we don't really know for sure, it is likely though). I don't honestly know if 64 bit is going to do tons for us, but a 20% faster processor, will definitely help. 4gb isn't needed at all, imo for Win XP. 2gb is useful however.
But what you say at the end is very true. The 1710 will do all you need now, and if you find you are satisfied with the system, you don't have to upgrade at all. And if you stress the system out or find some new game in 6 months that requires the G80, you have the probable option to make use of that as well. It would be incorrect to overbuy, but if you already know how much stress you put on a system, then I think you know what you are getting in the 1710 and what it's future is. The 1710 fits both, now and later.