Are old movies on blu ray worth it?

Hello, I have been at a video store recently and I was surprised to find really old movies on blu ray. I even saw Casablanca in there. I thought that the only movies that could be released on blu ray were the ones from the post-HD era... or at least, the only ones that could benefit from that format. So my question is: Is there a significant difference between such an old movie on DVD and on blu ray? I already have Casablanca on DVD, so I don't know if I should buy the blu ray. Do you think it's worth it? I ask because I think old movies are the best ones and if you tell me that it's a big improvement, I will run to the store right now and buy all of them...

Hello there, I'm a film student and I had a class on this topic last year, so I'll try to help you. There's a common misconception that old movies were recorded on lower resolutions than today... but actually, most of them were shot in 35 mm, which is higher than a blu ray, so, if the distributor payed attention to the quality, some old movies are definitely worth the money: Casablanca is one of them. I own that particular blu ray, and the image quality is nothing short of exceptional. I even read a review stating that it is probably the best blu ray ever. So run to that store and buy all the old movies you can find.