I thought Stellar Cartography was a corrupted technology. If I replayed a scenario, I would know where the good planets are ahead of time, so the AI was granted this ability as well, and as a result my motives changed. Instead of trying to play a game through in order to win on the first pass, I was pre-exploring, restoring and replaying, trying for a perfect game.
It makes the game more difficult to win on the first pass, and easier to win on a replay. This might be a good feature.
If it is going to stay as in GC1, then Stellar Cartography should be a technology the player can buy very early in the game, while the race is still on for the best worlds. It's placement in the tech tree will affect which size maps (and useful planet densities) that is worth persuing Stellar Cartography on. If you know it's gonna come too late in the map, then don't get it. Hey, this is starting to work