While collectors in general do not usually treat their hobby as an investment, the potential appreciation of collection value is certainly a sweet bonus for some.
From art to coins to stamps to movie posters, it is possible for any type of collection to achieve higher value over time. With movie posters, this is especially true for classics or movies with a huge fan base. Scarcity of material plays a part too, and sometimes sleeper hits or cult films with a limited poster print run can result in collectors paying a pretty penny for their posters.
Take for example the films Donnie Darko (2001), Lost in Translation (2003) and Drive (2011). Released just less than two decades ago, one sheet posters of these films are already highly coveted and significantly more expensive than their same-year release counterparts.
Wide releases with a huge fan base, such as Marvel superhero movies, also often have a correspondingly large collector base looking to own a piece of collectible from their favourite movie. For example, the first release posters for Avengers (2012) and Iron Man (2008) have amassed considerable value.
Of course, the collection value of a poster is dependent on other factors, such as whether they are original or reproductions, aesthetically pleasing, and whether they are in good physical condition.
For most movies, the best time to buy a poster is before the film is released, when its supply is relatively higher.