You can't just "buff" old oxidized gel coat and expect it to really shine... The oxidation is basically a bunch of pits in the surface of the gelcoat. You need to physically remove the top layer of gelcoat with sanding... Again, start with like 400grit and work up to 1000 then compound, and then wax...
I would try doing the above procedure on a small area so you don't spend a full day or two doing it, and see how it looks... Again, I suspect it will shine up like new.
My preference for the compounding stage is Meguiar's oxidation remover... it starts out kinda gritty but as you buff it, it breaks down into a finer and finer grit... It really works well... Then clean it off and follow up with a marine polish...