The only time I 'invest' real money in games is to purchase the game itself. I don't like spending cash on cosmetic changes when there's a lot of more tangible and important things that I need. I mean, if I manage to get in-game premium currency through events, then all is well and good. But I won't put anything more than my initial investment. Pivotal DLCs are different, though.
But if you mean in games like League of Legends, or Overwatch? No, I don't spend money in-game either.