This is another area where the AI needs a lot of fleshing out. Not only does it seem to go for planet value over anything else, it will not 'give up' on a planet it has decided to colonize even when massive military force stands in the way and other planets are easily accessible. If you blockade a warp point into a system and destroy any colonizers that come through, it will keep sending another colonizer forever. I've often seen it send colonizers THROUGH a system with a half-dozen or more colonizable planets trying to reach another system. Once in a while it will send a warship through ahead of the colonizer, but it will never, EVER, fleet colonizers with warships as escort. Nor will it guard a colony once founded. Slag a colony and it sends another colonizer, unescorted, into the same system with your waiting warships, and doesn't bother to defend it even if it manages to refound the colony.
[This message has been edited by Baron Munchausen (edited 06 October 2001).]