I've gone the labor intensive route on a couple of older boats rencently:

1) Fill all the scratches with either bogged matching gel coat (visible areas) or Formula 27 (bottoms), sand smooth with 100 grit.
2) Wet sand with progressive grits - 320 (patches), 400 (everything), 600, 800, 1000.
3) 3M Heavy Duty Rubbing Compound and a machine buffer (get a real one, not the $25 toy they sell at WalMart. DeWalt 849.)
4) 3M Finesse-It II w/ machine buffer w/foam pad
5) 3M Marine Wax

I did a 17 year old Hobie 17 and a 20 year old Hobie 14 in a day or so each. They look like they were just popped out of the molds. Shiny