The problem isn't really resolution, it's bitrate, codec, and effectiveness of the encoder. A sibling says dvds are trash bitrate and an old codec, and it's hard to argue with that... but some DVDs are better than others and many look fine on a large hires screen. When they put ten hours on a single disc, it's almot certainly going to look trashy though.

Would a bluray look better? Probably. Does streaming look better? Often, but not always; streaming likes to measure quality by resolution, but more pixels doesn't help quality unless it comes with more bitrate and/or improved codecs and/or improved encoders... And sometimes streaming has pretty low bitrate.