When you stand in a queue, you know how long you have to wait. It's fair as everyone knows their position in the line.
G+ is a queue where instead of letting people in according to how long they've waited they pick some people at random from the queue, even if those people have been standing for just a few minutes at the tail of the queue. Nobody knows how long they have to wait.
Limited invites would have been far better - same way they rolled out Gmail. The problem is that the crappy invite system is turning people off - they try their invite, it doesn't work and they don't come back.
I've decided not to bother any more with G+ right now. Maybe I'll come back to it in a few weeks or so but right now it just seems to be full of hard core geeks - the same people I follow on HN or Twitter anyway. None of my immediate friends or family are there so there's very little to keep me there.
But not opening it up - as you say - risks expectations that are too high as the buzz continues to build.
Mind you - I never heard anyone complain about the quality of the iphone after they waited in line several days before hand. Not saying the google+ will meet expectations in the same way. But you know - it's seems preferable to have maximal buzz than minimal in just about all scenarios.