No there is no trading up, the reason being that it becomes too complicated to figure out how many of what equals one or more higher level corals. That being said, there have been TONS of times in which someone with a higher coral with give a ticket or more to someone with lower level tickets.
As far as guidelines go, normally wicked does all of the "grading" of corals wo it would be up to him. We let him do most of it as he is our resident coral expert.