At our local IPMS show last quarter they guy who won best of show in the car category had one of the most amazing polishing jobs I've ever seen on a model. I chatted with him for a bit and he said he uses a cheapo clear coat from Walmart in a large rattle can. I was blown away.

Now, this material might not work on aircraft, I could see it filling in rivets and panel detail. But as far as being crystal clear and polishable (?) the results stood for themselves.