I feel a trailer hook is indispensable . you get so many short strikes with a spinner bait. if you don't use a trailer hook you're really missing out on some fish. You'll have fish take a swipe at your bait that you never knew were there without a trailer hook. Ask KVD, he never uses a spinner bait without a trailer hook.
As far as the trailer goes for a spinner bait I've been pondering that myself I use trailers all the time almost exclusively with jigs but I have never tried it with a spinner bait yet