Diamond Kote just isn't worth it. Ask someone who has a vintage car in showroom condition and see what they say.
A quality wax and glaze will protect your car just as well, and, for much less money.
Don't fall for fancy names like Diamond Kote, its just a marketing term and gimmick. In the end, if you protect your car with a good wax and keep it clean by hand washing it, that's the best way to have it look new.