In the early '90's i was taking apart and cleaning a lot of computers for a company that did that type of thing. It was amazing the failure rate on some of them that had a lot of dirt/dust inside. In fact we came across a bunch that had a "blanket" over the board, sort of like a thick layer of lint from your dryer. Evidently the components couldnt handle the change in operating temperature when we cleaned it, and would fail. I'm sure there are a ton of technical reasons for this, but basically i've learned that if its not broke, dont fix it. Especially if your potential buyer doesnt care anyway.