I think you are right that the constraints are what make it more interesting.
For the artwork, thinking about "how do I make this game look better" is a totally different question for retro art vs modern 3D AAA games. For a retro art game, its all about making it look the best for the number of pixels you have to work with. This is achievable by a single creative person with minimal technical expertise. How do you make a 3D AAA game look better? You need large teams of programmers and artists building a huge engine, which is likely constrained by their platform target. There are always more technology boundaries to push, which constantly makes older games look worse. But for retro games, the limit has already been hit, there isn't anything to improve on.