Not being an expert at all and not living in a county like the USA or even Japan where everything seems to be collectable at some point in time, I gotta say that the prices of modern posters, even if in near mint condition, seem to reveal that there is not much interest to be honest. In my experience, paying more than, let's say, €5, for most modern posters, let's say, from the last 5 to 10 years, it's usually a bad deal.
This may change radically as we move back in time, especially if we are only considering original editions used in cinemas. Stuff from the 90's or even from the beginning of the year 2000 is super rare in any condition, I can only imagine how many of those just went to the trash!
The matter of the short supply will only get worse since many, many movie theatres are already digital or going that route, it is much smarter to have a couple o digital frames (basically LED TV screens?) where you just load the posters you want to scroll every minutes and be done with it...