Legendary will not retain it's value. It is in no way "uber-elite limited", there are a TON of copies considering that you can still preorder it.
This will definitely not be a MGS3: Subsistence LE (even people who preordered didn't get it)
I'm a big halo fan (been one since halo 1, through halo pc, halo 2 , halo 3 beta, and soon to be halo 3), but even I can see that there is no reason for it to hold or become rarer simply considering how many have been manufactured. There might as well be a "Platinum Hits" version of the Legendary edition.