I'm very much with strapped rather than BB on this one. Very few of my films would be described as demo material, this would seem to rule out almost all older films even where they have good remasters. It would rule out all films that have only stereo or even mono tracks. Off the top of my head, I wouldn't want to be without bambi, the Dambusters, the hustler, the godfather trilogy, paranoiac, walkabout. The list would go on and on. I imagine it would also rule out silent films like nosferatu or metropolis. Conversely, a large proportion of the contemporary blu rays which are of reference quality are dire films. I wouldn't want to own transformers, avatar or iron man 2, again off the top of my head.
OOI strapped, what are some examples of films you have bought for research purposes?