I like to think that the fact that they keep re-releasing the games is a sign that they are still interested in the franchise, and thus in making new games, in near future. Maybe just a wishful thinking but...
I don't think it's a sign that they're still interested in the franchise. Heck, interest may not even be part of the equation. If anything, it looks more like they're pulling in as much profit from what already exists of the franchise.
If they truly were still interested in the franchise, wouldn't they show something more of it than just re-releasing the same game on a different console/port? If this were the case, then I could argue that Nintendo is still interested in the "Mother" franchise.
This isn't to say that I'm cynical about all this. I just wish they'd actually show a more obvious commitment to the franchise.