The Lego Rock Band won't be added to the Lego complete club because it doesn't really fit into the traditional Lego theme. Retail and PSN games aren't mixed either, as that would make too many requirements to join and it'd be a bit too much having 10+ games in there.
Hey, I dont know if you would be interested, but There is a project going on the level promoting thread. If you would like to be apart of it let me know. The info link is on the first post of the thread.
For both of the first two questions, it's really what you want it to be. I think I have stayed away from platinums, because if a game have a specific trophy that is hard, it tells more accurately what you mean. But that's just my take on it.
For the most shameful trophy, I guess it's supposed to be a trophy you're ashamed off. I platted Hannah Montana during a platinum competition (it's a really fast plat) so I guess I have some trophy from that game as my most shameful.