Minds goes to rot if one does not use them. I would treat Mensa test as a good way of keeping the mind healthy.
I had no idea what Mensa was before stumbling into this site. I do believe, I am far from genius but I believe, we are capable of great things genius or not. One thing the genius have statistically in common is their abundant energy. There is a link between health and performance. A mind that is alert is basically a healthy mind.
Be happy and enjoy the Mensa challenge test and you might find a small genius in yourself.