MrKite wrote:(there's no difference in them from DVDs other than the sound quality from what I hear)
You were misinformed. Audio tracks require minimal space. The only thing Blu-Ray really does compared to DVD is: carry more data per disk.
So with movies that were released AFTER Blu-Ray technology was commercialized, it's "better" (arguably) to buy Blu-Ray because you'll get the best possible resolution, if you have the TV for it AND if you can see the difference, a lot of people don't.
The first time I really saw a difference was when I compared a Stargate Universe DVD with its Blu-Ray equivalent. The DVD gave me what I was used to see: nice resolution, clear image. Then I inserted the Blu-Ray, I was blown away. In the Intro, you can see the SG:U ship up close. On the DVD it was ok. On the Blu-Ray, the amount of clarity/detail/precision was staggering. If your movie wasn't filmed in HD? Waste of money.
So what else does Blu-Ray potentially add to your film?
-More soundtracks: more languages or more sound quality options. This is trivial and borderline useless to most people.
-Legions of previews: aka "I WANT TO WATCH MY MOVIE, STOP THIS ALREADY!"
-Tons of extras: Outtakes, making of's, deleted scenes, alternate endings. You know, the stuff no one ever watches.
-Technical headaches: Blu-Ray firmwares have to be updated regularly, else you end up with unreadable disks. Furthermore, loading times can be extremely annoying. Finally, if your reader is cheap, it will most likely NOT remember where you were when press the STOP button (most DVDs remember unless you physically remove/change the disk), meaning you will have to go through the boot up, previews, long menus AND have to scroll up to where you were to resume watching.
So what's the advantage of buying an OLD movie in Blu-Ray format, especially if you already have the DVD? Well, you get to make someone who is rich a little bit richer. That's it. You can't go back in time and upgrade a movie to 1080p if it wasn't filmed in 1080p.
Old movie? Get the DVD.
New movie? Your choice, but if it's not a visual-centric movie, I generally get the DVD and save 10 bucks in the process.