Not sales. Ratings. And you can only rate the game if you made a purchase. It's a 15 year old game, so it will be "new" to a lot of people.
What are you counting then? Number of ratings submitted (not everyone who buys a game rates it), or the average rating (newsflash, just because you like a game does not mean Joe Otherperson will, too)?
In both cases, I do not believe the result you're getting is in any way representative for interest in the genre itself; especially when we consider that the market you are watching is very, very limited and has no overlap at all with the traditional venue for space sims.
Also, where are you getting the impression that people think it's a new game, when it is pretty clear that it's "just" a rerelease? In general, the first people who buy those are the people who knew the original; given that it's a 15-year-old game, that market isn't very big to begin with.
Saying that Diaspora doesn't count because it's free is not a good thing to do IMHO. Sure, there are more people interested in free stuff, but you can use free stuff to gauge interest in the genre; This data can then be used to estimate how many people would be willing to pay for similar games.
But damn it, I want to see an epic game with today's technology, something big and fresh and cutting edge.
Alas, the best way to get there right now is to get a few like-minded people together, build a prototype using UDK, Unity, CryEngine or whatever, and then shop it around on kickstarter et al to get funding for completion.