I think it's a matter of time and/or money for some people, how many weekends and dollars you are going to devote to a strange venue to check it out and work your way up to the full performance level, vs. spend the time and money where you are comfortable, and already in a system of earning points and titles. I know I had a scenario where I could start at a higher level, (not THE highest level), with my already experienced and trial-savvy dog, and I was happy starting there. We didn't clean up, and the courses were challenging for us, and it showed me what I would need to train if I wanted to continue entering that venue. I decided not to because I liked my many NADAC trial options more. If I had had to start at the lowest level I don't think I would have tried the other venue at all.
I think they had a rule that once you Q'ed at a certain level you could not go back down to a lower level. I would not recommend that, as I don't see any reason for it and it would be difficult to police.
I don't know how you would enforce "showing proficiency in another venue".
I'm up to 4 cents now!
Heidi in NH