What is the benefit of getting accepted into Mensa?

Speaking as a member of Mensa for over 30 years, I would agree with the above expressed sentiment of 'camaraderie and kinship', but not with the 'like-minded' individuals. One of the beauties and attractions of Mensa is that everyone is 'different, with no two minds the same'. This gives rise to a plethora of ideas and philosophies that one does not meet in everyday living, or even everyday 'reading'. One's own ideas can get crushed and ground underfoot, only to be rebuilt and improved by one or more people who see your ideas with a different mindset. There is also the 'fun' side and humour that is often 'out of this world' or just plain 'joke of the day'. We are ordinary people.

I was a member in the mid-'80s and saw no benefit whatsoever except for bragging rights. Bright people may be found easily without paying dues for the privilege. Furthermore, there are several kinds of intelligence (some psychometricians say seven), and some people who are smart one way can be reeeeally dumb in others. I found my fellow Mensans to be no more attractive than the outsiders -- so I went and played outside.

No idea, other than the benefit that is present in joining any group of like-minded individuals -- camaraderie and kinship.