I think that I'm getting closer to the configuration I want. I'd like to hear what you think.
First, I think I'm going to play on a huge map, against five races. Huge map has 144 sectors which, divided with the number of players I put in the game, gives an average of 24 sectors per empire. Gigantic map has 256 sectors, so if you play against nine races, it means that, theoretically, there are 25,6 sectors for every empire. So, these two configurations should give about the same game feeling, it's just that I don't have to bother with four other races, and frankly, I think that five opponents are about enough. Just remember Star Trek BotF, in Star Trek universe there were only five races altogether.
I've experimented with different planet and star configuration. The following seems to be interesting. I put stars to abundant and scattered, and planets (and habitable planets as well) to common. This way I no longer get dozens of 12+ class planets around me as when I put habitable planets to abundant, but I get enough to create a fine empire. I am still very inexperienced player so I don't know if computer usually generates maps this way, but this configuration seems to lead to the creation of rich star systems with two or three high quality planets and you can easily find such systems, yet most systems have only one average habitable planet, or none whatsoever. This looks like a nice balance. If you're into this, try it out and tell me what you think.