"Polishing" question.

I have an 18 year old Buick that is always parked outside; the exterior has received minimal "maintenance" over the years. The finish has a level of grime that takes "2 wet fingers" to get through. I believe the "clear coat" is fine (so I am hesitatant to start with rubbing compound, but I am listening). I am willing to invest in an electric polisher to assist with the process. What materials/technique/process would you recommend to me to revitalize my car's finish. The car market being what it is, I think I'm going to hang onto my car longer than I originally expected (basically, as long as possible). Thank you for sharing your expertise and suggestions with me!