As far as new movies are concerned, it is virtually impossible to predict which one will stand the passage of time. Which is why, as Schan said, you must collect what you like. The reason BTTF is in demand is because it has become a classic that will probably be cherished for generations to come. Again, I say probably because what is fashionable today could be obsolete tomorrow, but it is still much more collectible than say, Transformers. The price reflects the demand. Since there seems to be a very limited amount of re-release BTTF posters out there, its price is basically what the sellers charge and what you are willing to pay. It could pop up on Ebay tomorrow and the price could drop. If it does, I assure you it wouldn't drop too drastically, because the Struzan design is in demand no matter what. I am a completist, so I collect by theme. It helps me organize my collection, and I believe it is a better way to ensure your collection holds its value. If you want to give yourself better chances to build a solid collection, watch the trends, project yourself 20-30 years forward and try to imagine which actor, director, movie will still be relevant. Grindhouse is not a bad choice. I think Tarantino will be remembered as a ground breaking director. Cameron could be another one. Fincher maybe.
Enjoy the hobby, and stay away from Mel.
Thierry
