Do you know what recursion tower does, or is that one that doesn't have a function either?
Noted. I'm not sure either, as it's the next thing I unlock
Update: I've unlocked it. I'm not quite sure what it does still, but when it gets to a new highest rank, my money increases by quite a bit.
Update 2: Once level tower hits 9, you get a huge increase in monetary gains. So it probably is such a minute amount of bonus until it gets to higher levels