I think the focus on new comers to Mensa may reduce this. I also think it would depend partially on why Mensa people are ineffective. If there ineffectiveness is set, or due to something that we don't have a comparative advantage at fixing then yes we shouldn't focus on recruiting them. However, its possible that many of them are ineffective due directly to rationality failures, or some other problem that the LW community could help fix (e.g. they lack something to protect, but would find existential risk reduction very compelling if they heard the arguments for it). In than case Mesna would make a good recruiting ground.