Not a lawyer but... if you have the DVD its legal to make a backup digital copy. I am thinking the same thing. Most recent movies are available for under $20 per DVD - and there are tons of deals. You can get the 4 lego movies for $5 on DVD on Amazon right now. A "Tom Cruise 10-Movie Collection" is $12. You get the idea. Get the DVD. Make a legal backup. Keep the physical DVD in storage. You now "own" the movie (or T…
The vertical resolution of a DVD is either 480 (NTSC) or 576 (PAL). This usually matched the visible vertical resolution of the TV you were using. A 1080p screen has 6 times as many pixels as an NTSC DVD. A 4k screen has 24 times as many pixels as an NTSC DVD.
DVDs are not well-encoded, and the sources are typically poorer, too.
DVDs store MPEG-2 Part 2 (H.262) video streams. It's an extremely old, inefficient codec. (It was published in 1996! Next month, it'll be 30 years old!) It looks best when the encoder is given a bitrate limit north of 20 megabits per second, but DVD-Video has a hardware limit of 10 Mbps, and that includes the audio and subtitle streams. Most video streams on DVDs get 4-5 Mbps. MPEG-2 also isn't a very good codec; no matter how much bandwidth you get it, it's never really considered to be “transparent” (that is, encoding artifacts are always visible).
If you take a Blu-ray copy of a film (FHD or UHD, doesn't really matter), scale it down to SD resolution, and run it through a good HEVC (H.265) encoder, you'll usually find that a DVD-equivalent encoding takes about a third, maybe a quarter of the space. Or, if you go the other way and let the encode take as much space as the MPEG-2 one on the DVD, you'll almost certainly see an obvious difference, particularly in action scenes.
Starting a physical media collection? Fantastic. Good for you (seriously). But get Blu-rays wherever possible. You'll mostly have to forego the thrift shop, fine, but if you're ever actually going to watch the film, you'll vastly prefer it.