I did that in the past too, just to boost my Steam Level. But its kind of waste of money, because I don't benefit from the benefits its providing me anyway. One can already add 250 friends and upgrading adds 5 more slots per lvl. With every 10 lvl more showcases can be added to your profile (but mine is private anyway). I stopped at Lvl 69 because I realized it makes no sense (but it kept going up on its own).

Here is a nice post I found about Steam Profile Levels: https://steamcommunity.com/discussions/forum/30/691998095298452123/