the best thing to get it back to original shiny black is a product called ".
303 Aerospace Protectant "... the last time I wiped my dash down was at LFW2002, which was June 1st, and it is still looking as good as the day I cleaned it. I know some other people on this board use the same stuff, and can testify how good it is. Also, all the guys in my dads Porsche club swear by it (including Jerry Seinfeld).
As for the clear plastic... I use a glass cleaner that I bought from
Preformance Products here is the page of the actual product
Fleet Glass Cleaner . I also use the
Plexus Plastic Protectant to keep it looking good for a long time.
Good Luck...