I still want Sanatarium at 6 Debt.
I'm simply not convinced by your reasoning that Sanitarium would be too strong for 4$. It sometimes will be better than Village. It sometimes will be worse. It will be better more often than worse. Big deal, it costs more. It also gives the gaining bonus. Only a few times, though.
Again, if Sanitarium has to compete with Worker's Village, Wandring Minstrel or Port, it doesn't need to be just good enough for 4$. It's fine if it's a strong 4$. Neither a Village, nor trashing, nor draw-to-X are inherently game-winning effects. You need to be able to play them right. And if a strong card leads to more interesting strategies, which I think Sanitarium can, I see no problem.
Don't get me wrong, there's nothing wrong with a cost of <6>. But there's nothing wrong with a price of 4$, either. So I'm going to stick with the more simple thing unless something made me believe that costing Sanitarium at <6> somehow made the card more fun, which I doubt.