In a contemporary car, gloss overcoat is fine. For older racing cars, say sixties and earlier, the cars were really never super shiny, nor clearcoated, so super gloss really is not appropriate in a model (though some folks still like to see them that way.
When I do an older race car, I try to get a good, polished finish- no overcoat, then try my best to get a good decal job. Decals do not really need sealing as protection, so if they look okay when applied and dry, let them go that way. Only if there are problems do I do any sealing. btw, Testors glosscoat can be polished when thoroughly dry (several days), and a little polish takes out some of that super gloss.