Simple things like manuals, original box art and concept art images are the bare minimum to include. Cut content is something I like to delve into and I welcome any collection that includes those. Developer commentary in audio form can be interesting , but then I really have to care about the game(s) enough to listen to them. If there's a prototype/beta of a game that's vastly different from the final product, then it makes sense to include that as well if possible.
I do agree with the interactive museum aspect, those are neat if done right.