We are discussing this one internally. For me, it takes away from the sense of discovery. Every planet has been 'tainted' by pirates already. A rare untouched planet would have a really mean something. The downside of many uninhabited planets is the risk of constant colony rush, and fair distribution of these planets. There is likely a sweet spot somewhere inbetween. I am interested in more opinions on this one.
Well, I would like it.
Currently I have 2 colony ships per Kol, and the Kol always clears those planets faster, then the colony ships get antimatter to use their ability. I'm always low on credits in the beginning, since I use all my money on mines and planets improvements.
So, I don't think I could get really faster with colony rushing, since even if there were no pirates, I'd a hard time to get enough credits to finance it.

What I would like if some of the planets you discover would already be inhabited by a neutral player, i.e. the pirates. Would change the exploring part a bit, if you've to bomb the planet before you're able to colonize it.
And imho it would also be nice, if those dead asteroids weren't colonizeable. They don't give resources, tax, logistic points, only tactical points. It would be imho more fun if there were still some uninhabited areas besides the sun in the late game, and those dead asteroids would be perfect for that.