Number one collectable kit for me all time would be Neal Peart's kit from his first time performing live with Rush. That show happened to be in Pittsburgh, and all in all, that would be the kit I would place as number one on my list. That kit represented the beginning of a forty+ year career and a better-than-most chance that anybody that was asked would mention him as the best of all time, at his discipline.
Number 2 is anything Stephen Adler played on, live.
I see collectable as something that was used by a successful drummer, to do something important in music. Not a randomly made kit that happened to be so unpopular, they only made a few of them at the time due to poor sales. Then fifty years later, they are only cool because there weren't that many of them made and everybody wants something nobody else has.........