This is exactly the case. If you only game and surf then you don't need the Quad BUT if both CPU's are going for the same price 2nd hand then the Quad is the one to go for.This. I did exactly the same, then a week later I thought - this is a waste of cash and promptly sold it on again!
My 3.8Ghz E8400 is more than enough for my machine - but I only really play games and surf the web.