I find reinstalling the system to be good test once in a while perhaps once a year then, it proves to me at least that if my harddrive were to die right now my backup plan would work and that I could continue, but one would need to make sure that one has either the restore disk, or a copy of the XPcd of same type, all ones drivers, and copies of the programs one needs so that they too can be reinstalled and that ones data is stored elsewhere, in short, it is a lot of work, and the updates need to be done too, but at least one is sure that the rubbish is gone, period.
The trouble with the above idea is when one has paid for some protection, in that case I would wait until the protection contract has run its full length and then reinstall, and then buy more protection. Anyways, the idea even if you don't follow it here, does make the reader think "am I in control of my system or stuck with it" which is why I am suggesting it here.