The touch screen problems that I had did disappeared suddenly and reappeared in worse way. I never replaced touch acres of my N900 but was lucky enough to find a seller that did offer 2 N900's for €30,- a piece. Used backupmenu soon after buying. It's not difficult to replace the touch screen just don't brute force and the right equipment for it.
http://m.youtube.com/watch?v=aVEHm325-z8