As one of my all-time favorite movies, getting it in 1080p HD for my home Plex library is great. I loved the book when it was first published, and I've seen the movie on TV several times. Now having it readily available, anytime, for the "big screen" in the livingroom, or any other screens... well it's just more than worth it for me.
Another HD movie I recently bought was African Queen with Bogart & Bacall. I loved that early 50's movie, but had only ever seen it in black & white or on the pathetic color TVs of the last century. It was so much better in HD on a Blu-ray disk.
As a bonus on that disk, there was a short article about the difficulty of restoring old films shot in Technicolor. Technicolor cameras were huge cameras, because they used three rolls of film simultaneously... one each of the three basic colors. Three cameras in one, to get better color than a single roll of color film could provide. Theaters then needed Technicolor projectors with three synchronized projector lenses to blend the three colored film rolls together.
To digitize those old films, restorers had to find the best individual reels of the three colors, and synchronize those, frame by frame (including the sound), as they restored each frame. It's a far tougher process than I ever realized, and with Technicolor, three times as difficult as with B&W or other color processes. I'm glad there's enough of a Blu-Ray market to justify the cost of such a difficult restoration on old classic films.