I prefer the tiered approach. I currently have 12 of these, and i've bought in the 70s up to 100. If this breaks 200, i'll definitely sell off a few in the next week or two, and may sell a few more up into february if the movie creates a frenzy. Last years MF 7695 is a prime example of what might happen to the At-at. I believe the MF peaked around 260 (yeah a few may have sold over that, but not many) and then when the new MF was announced prices pretty much plateaued. After the new release, it's been sitting at 235 since and it hasn't really risen like the other sets. I really would be shocked to see the AT-AT go for 300.00 and hold at that price. Even MF 7454 has pretty much plateaued at 350.00 and that's been out for since 2007 I believe. A decent peak will probably be within the next few weeks and while it could go higher, I doubt it goes MUCH higher.
Other At-at's like 8129 currently sits at 245. The ancient one 4483 while in the 500 range would have had to been held for a decade. The motorized one is kind of it's own animal, and that sits around 700. I don't see this version following in the footsteps of the motorized version.
Personally, I don't view most star wars sets as super long term holds since rehashes are too common. Just look at what happened with the A-wing, Droid Escape, Hoth attacks set, Homing Spider Droid, etc. They are all getting rehashed next year, and will be out soon. AT-AT may have 2 years before the next iteration, but it will definitely have a new iteration in some form very soon.
Since I have a son that likes to build, I can pretty much flip two at-at's in the next couple weeks and take the profits to a lego store on January 1st, and buy a Brick Bank for free with the profit play money. Not a bad move, by just picking up a few more at-at's over the last few days.