I reckon it is good policy to do a complete reformat and reinstall of Windows about once in six months. Since I run ME, I have to do it more often than that anyway when the system become completely unusable. I think I must have done it at least half a dozen times in the past 18 months.
We all accumulate a lot of clutter that we don't really need. If we do find that we need it, it is usually simple to reinstall.
If you go back to a barebones system, you will be amazed how much faster it is to start up.