I think you'll get more response to this question on another board, like the AR Discussions board in the AR15 "community".
IMO the prices of pre-ban firearms and magazines are roughly 50% - 100% more than their actual worth, and they will come down after the ban expires. They're nowhere near as inflated as transferrable machineguns. The price of post-ban configurations will not be affected at all.
In a way the ban encouraged development of some muzzle configurations that might have not have ever seen the light of day if the ban had never been enacted. I'm sure you will still see plain muzzles on target rifles, and some of the highly effective recoil compensators that were made specifically to comply with the ban. The difference will be that they will not have to be "permanently" attached any more. You'll actually be able to remove your brake or flash supressor and take off the gas block easily without buggering up the muzzle threads.
There won't be a stampede of people wanting a bayonet lug because there's really not much use for them anyway. An ArmaLite sales representative told me that cops (who can presently buy newly manufactured pre-ban items) often insist on having the lug even though none ever carry bayonets.