I'm going to stay firm on my statement. It's a huge leap. I know that it seems like it isn't much, but take a look at this page: http://en.wikipedia.org/wiki/File:Ve...Standards4.svg
Now, compare NTSC resolution to 1080p. NTSC is 640x480 (standard for most DVDs), while 1080p is 1920x1080. That's 6.75x the number of pixels. It may not seem like that big of a deal, but it is. There is so much more detail when you have that much more raw data. I see things I've never seen before in movies on blu-ray that I've watched dozens of times on DVD. It really is that staggering of a difference.
Also, I've noticed that lots of movies are now changing as blu-ray has become more widely adopted. Directors will often think about how things will appear on a home television and will make the movie accordingly. There's a lot of stuff in movies now that I think will be lost on DVD, like text on a letter or car that is readable at a higher resolution, but will likely get lost at a lower resolution.
There's some decent upconverters out there, but they all have to guess at what those other pixels should have been. It may not look horrible, but it's not going to be nearly the same.
As for the audio quality, I don't think most people have a nice enough sound system to tell between compressed 5.1 on a DVD to the uncompressed 7.1 in most blu-rays, but it's still a huge leap in quality, and if you have the speaker setup for it, you'll be missing out.
As for discs, my wife and I don't buy blu-rays. We don't buy movies in general. We'll rent if something is interesting and that's about it. I hate having a shelf full of discs. It drives me nuts. The movie industry needs to offer a service like steam. Ultraviolet is out there, but has way too many strings attached at this point, and is still just streaming. You can't download you movies to a computer and watch them whenever you want. And they also have a maintenance fee after a certain period of time, which is dumb. I don't pay a maintenance fee on any discs I own, and if steam can offer "free forever" after buying something, then a movie service should be able to do the same.