Haven't joined Mensa. I did once go to a Mensa party. Most people sat around doing math puzzles, except the one (unmarried) couple, (seemed they had just met) who probably were about age 45, who made out with full on tongue action and the whole bit. (Everyone else seemed to ignore or tolerate it, so as a guest there, I ignored it too.) I found the party unappealing, although, there were some interesting people there.
Toward the end of the party, a few college age people came in (I was in my 20s at the time too, although, age didn't matter, the most interesting person at the party for me, was 91) and livened things up a bit, only because the other people there perked up somewhat and began chatting more animatedly once the younger ones walked in.
Basically some of them had mentioned earlier in the evening, that they were bored with Mensa because there were not enough young people who were members. (That was the subtext I took from their statements.) Kind of a reverse ageism (preferring people of a different age) - from the old.
That is my one experience with it though. I think it will vary by local chapter. Also there are national things to do and events to go to. For some it was a question of affording the annual membership dues.
Honestly if I had hands on my qualifying test, which the schools had long since gotten rid of, or had a chance to study for the MAT (Miller Analogies Test) since I am too long out of school to be up on the math formulas most IQ tests rely heavily upon, and then a chance to find and pay a qualified administrator for the MAT, I might have gone for it. As it was, it wasn't that worth pursuing, for me. I'm not big on parties though.
The chapter also had game nights and many outings (ETA: including cinemas and restaurants as a group), and at the time I was trying to be more social and I would've met more than who were at that rather small gathering, if I had stuck with it. (I was invited to attend regardless of joining.) But I didn't, for whatever reasons.
I'd say try it, can't hurt to try. Phone up the local chapter head and ask if you can attend some of their outings before you join.
(ETA: They did not seem arrogant to me at all. They were open and welcoming to me.)