I'll have to partly disagree with you there as I've seen plenty of cars which weren't Lambos sporting green calipers that didn't look tacky, ...some Mercedes, Porsche, and a Nissan (R35) GTR just to name a few.
It all depends on the cars colour I'd say to how good it'll look although I'd imagine the type of car & size of caliper does have some baring on it.
Merc, can't see it looking good.
Porsche, only on the track versions.
GTR, maybe, but it'll still look like tacky rice.
McLarens can get away with it for some reason too though.