I've generally not had an issues joining random parties kicking me doing SH or VH UQ's. I haven't done any "high end" stuff yet, but I will do so with an alliance.
That being said, I am being very picky about the alliance I join as I have spend many a time in my online games of old jumping from guild to guild trying to find the right one (and I am not looking to repeat that due to some pretty bad interactions it he past and ain't no body got time fo dat).
I also solo alot largely because I am doing some daily quests and half the parties aren't even doing the ones I need.