I'm sure there is some truth to that, but as in all things, it is not the entire story. I have been collecting movie posters for 20 years now (I started in 2001), and believe I have put together a fairly nice collection (at least to me). I did a little exercise right after HA's last signature auction. I already owned 84 posters they were selling (I wasn't selling them but I owned them). I don't mean to be rude by giving numbers out (Mel used to do it and I hated it), but I'm trying to be precise. I added up the amount those 84 posters sold for ($216,034) and compared it to what I spent on them over the last 20 years ($53,634). That's almost 4 times what I spent. Even accounting for inflation, that is still a pretty good markup.
I did the same with the Mondo sale, and fair enough, came up with a total that was close to 10 times what I spent. But I also bought those at drops and never from secondary markets. So yes, prints went up way more than posters. Way. But to say that posters are flat, imo, is not true....
First - I like the fact that you used an 84-piece sample size instead of a small one, definitely makes it more reliable. But of course even that doesn't tell us a complete picture. This was from a Signature auction, so it
should represent more cream-of-the-crop items, and not a bunch of lower-valued items that will weight the return average down. Also, you've always been the king of "someone gave me 14 rolled Revenge of the Jedi one-sheets" type stories, so no idea how many of those type purchases are included in your sample. Plus we have no idea the time period that you spent the money (if you purchased all 84 pieces twenty years ago, you're looking at just over a 6% return a year, not exactly setting the world on fire. If you purchased them all last year and they have increased 4x in a year, kudos to you sir).
And of course in picking a Heritage auction (or any single data point), you might be including sales that would be difficult to replicate. Taking a quick look at their top 20 or so sales from the last auction, I don't think you have any of those pieces, but scanning down at ones you likely do I see a very strong price for Forbidden Planet ($15K, double the recent Bruce price), an incredible price for an ET Bike poster ($6600?!? - is that a new record? That's more than triple the price Bruce got for his in the record-setting Halloween auction), $9900 for a Thunderball six-sheet also seems much higher than normal, $2000 for Raiders of the Lost Ark, etc. I'm going to guess there are probably some on the low side also, but unsure what they would be.
In comparison to the Mondo price increases (10x your investment in a much shorter time frame), it just helps the argument that movie posters lag other collectibles markets (Mondo being more an art market than strictly movie posters, I know several people who buy Mondo items for their collection and as of yet, I haven't been able to convince them to start on "regular" posters - but maybe that is a good thing, less competition.
As to the "why", I have no idea why they seem to be lagging. Heritage certainly seems to be doing a great job in advertising and getting the world out, and people all over the world love movies. Maybe there weren't enough places to source originals years ago, and so it's out of the minds of people now? No "rookie cards", or continuing sets to get? Maybe that is one of the hooks Mondo has, they continue to make posters in the series so people stay interested. The continuing demand of Star Wars seems to be the one thing you can count on right now. I will say that the discovery of fakes in the horror market about a decade ago, rocked that market hard and prices fell for for a few years, and that was always viewed as the bluest of the blue-chips in the poster world. And while I love those posters, I always found it strange that they would command so much more than the Casablancas, Citizen Kanes, and the like. And while 30s-40s horror seems to have stabilized and maybe on the rise again, it looks like the 70s/80s classics are the really hot spot right now (which again comes back to Star Wars).
As to Vick who asked what collectibles have gone through the roof? I'll assume you've been under a rock and didn't see the $10 million dollar Mantle rookie sale, or the plethora of comic books that have shot through the $1 million mark. A Magic the Gathering card recently hit the $500K mark and some Pokemon cards regularly hit six-figures also. I won't mention video games or VHS tapes since we have other threads on those, but we certainly seem a long ways off from any 90s poster hitting the six-figure mark.
Still think that eventually, others will see the awesomeness that we do in vintage posters.