There is a host of problems and it's not IQ related. Vote exchanges, vote bots, et al - the entire upvote economy is for the lack of a better word, corrupted.
People want shortcuts and sadly, others have created services to profit from them. These services then become the only way to succeed and true content creators will eventually give up.
So rather than making it harder to sign up just stop the services and bots and keep it about people posting, commenting and upvoting rather than tools or automation.
Algorithms aren't going to fix human nature. And people LOVE a shortcut to success. Once they realise there is no shortcut, they'll move on or wither and die.