I've been to a lot of AUG/ACEs, but for the last 6 years of them, I've been working for a partner, so some of the reasons for going are different, so I've got two sets of experiences!
As an Atlassian admin, pre-Adaptavist, I went to a lot of the London AUG/ACEs. Early on, I found that some were not good - when they were run by partner companies, you didn't know if you were going to a meet where you got a series of sales pitches, or something actually useful. But even when you got a set of sales pitches, the time between them was great because you got to talk to other Atlassian-using people who did it differently to you. The way they work, their ideas, and, frankly, the fact that most of them are just simply people in tech who you like, works and helps. You listen, you learn and you meet new people with some (vaguely) shared interests.
Things have moved on. Atlassian asked partners to stop doing sales at ACEs. Here in the UK, they did. Partners don't do talks unless explicitly invited by ACE leads, and we don't swamp them with people either. For me, whether I've got my "partner" mode engaged or not, this is great.
TLDR: To answer just your original question, I've been to about 1/5th of all the London AUG's since 2008, and every single one of them has found me new and interesting people to talk to.
