The fact that no matter how brilliant your idea is it's basically got a week in the limelight and then will be forgotten forever isn't super conducive to using LW to seriously discuss difficult problems.

I think that's fine. Public forums in general aren't proper places to seriously discuss difficult problems. What they offer is width, not depth.

Your complaint is really that there are not enough smart people who are willing to spend a lot of time and effort grappling with the problems which you are interested in. That's a very common complaint :-) and I don't think this problem can be fixed by fiddling with the structure of a web site.