To other intelligent people, my impression is that Mensa membership mostly distinguishes the subset of "intelligent and pompous about it" from the larger set of "intelligent people".
My experience seems to support this. The desire to signal intelligence is often so strong that it eliminates much of the benefits gained from high intelligence. It is almost impossible to have a serious discussion about something, because people habitually disagree just to signal higher intelligence, and immediately jump to topics that are better for signalling. Rationality and mathematics are boring, conspiracy theories are welcome. And of course, Einstein was wrong; an extraordinarily intelligent person can see obvious flaws in theory of relativity, even if they don't know anything about physics.
Mensa membership will not impress people who want to become stronger and have some experience with Mensa. Many interesting people make the Mensa entry test, come to the first Mensa meeting... and then run away.
My experience with Mensa was similar to yours. I joined, read a couple issues of their magazine without having time to go to a meeting, and realized that if the meetings were like the magazine they weren't worth the time. There was far less original thought in Mensa then I had expected.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
(I plan to make these threads from now on. Downvote if you disapprove. If I miss one, feel free to do it yourself.)