More than likely, if I already own the original, I'm not gonna spring for a remaster. Now if it's a complete remake, like Resident Evil and Metroid: Zero Mission were, then yeah, I'm all for that. When done right, those kind of remakes can breathe new life into a loved classic.
That said, if I don't already own it, it is nice to have that HD option out there. But it's not worth it if the development of these remasters are impeding on the development of new games.