And then there's the fact that this blog post just convinced me to buy this game.
I love wonderboy, I think it's extremely underrated and is as classic, and timeless, and as mechanically refined as Super Mario Bros. and Zelda were on NES. Master System just had so much less market penetration that Wonder Boy is now nowhere near the size of those other franchises, not because it lacks the merit, but because it lacked the publicity.
I had thought this was simply a "hand the IP to some new guys so we can milk the cash cow" when I saw the news that it was being made. The fact that these guys give this much of a damn has convinced me to pay full retail, I want them to be able to keep doing this kind of work after this game is done.
/my 2 cents
Somewhat separate, but related, I remember one of the video plugins that would accept external images as replacements for in-game textures.
Anyhow, I agree that for at least some games, replacing parts of the code makes getting the game running with some degree of improvement easier than completely re-implementing it. On the other hand, I like the idea of reverse-engineering the original binary, and along with an engine re-implementation, providing documentation of how the game originally worked. I think of it as a kind of software archaeology.