The best mono will usually come from LD digital tracks because of higher bitrate and the fact that most were taken straight from a film print. DVD mono is usually added as an afterthought and is very compressed. (DD 2.0 or 1.0 96-192 kbp/s) With that being said, the best DVD mono titles I can think of are Jaws, any Bond pre-1977, Criterion titles, and especially classic titles by Warner Bros. Warner is the studio that always presents even their most bare bones classics in mono. You can spread the signal to the L and R channels on some receivers but not all the time. (Learned this the hard way on my old school's receiver)
Mono should be heard only when there was a specific mix for it. As we know with SW there can be a world of difference. But films that were always stereo would only have had a fold-down or usually older equipment that could only read the safety mono track on the 35mm print.
What I don't get is the desire to remix mono into 5.1. Especially on classic titles. 24 bit audio on blu-ray should mean a more clear presentation of the original theatrical audio. The Manchurian Candidate should not be in 5.1 DTS HD-MA. OVERKILL!!!
This all carries over into music too. Whenever I play a mono record I have to plug my phono cables into a double-Y connection and then run that into my stereo receiver. That maintains the mono signal while playing through two speakers and reduces stereo noise. (I do this because my receiver does not have a mono switch.) Look up any album that you know very well that has a mono mix. You will hear significant differences if there was a true mono mix, and some variations if it was a fold-down.
The simplest way to go mono vs. stereo is The Beatles catalogue. Please Please Me through The White Album were mixed and released in mono. Starting with The White Album the band started mixing in stereo which is why that album has an alternate previously rare mono mix. For all of their early albums, the mono versions were mixed by the band and producer and feature clear elements in one channel. The stereo versions were done separately by studio engineers weeks later and have the vocals in one channel with all of the instrumentation on another. Pick any track on any of the early albums and do a listening comparison.
I will say that discovering many of my favorite things in both film and music were originally mono blew my mind. The Beatles were meant to be heard in mono, which means my childhood of hearing stereo Beatles was a lie...which in turn would mean...that yesterday was a lie....