I cleaned up my family's dinosaur (Gateway Profile 6) about a month ago and after saving the critical files, re-formatted the hard drive and re-installed the software as well (as I do every so often).
Brought it back to like-new speed.
Like all of my computers, when I bought it, I bought all of the high-end hardware available at the time, so I have found so issues that make me want to get a newer one, yet. When I get a program that I need (or just want badly) and it says my system won't run it...then I will get a new one.
Either that, or when I stumble on to money that I have no better use for.
But until then...I have a saying that I live by and offer it as supporting advice for this thread...a clean computer is a happy computer.