Readyboost is a solid technology for slower PC's . My theory is this, anything that boosts performance is a good thing. I use a 4 gig Cruiser stick in the back of my system and I just forget it's there, works nicely.
Does it helps? I dunno, maybe only 1 percent. But that's a point I'll take.
Just my 0.02 cents, you'll get more bang for your buck with less ram on your system. 1-2 gigs see a noticeable increase I've been told. But it won't hurt.