Personally I believe the purpose of life is to insure the survival of life, the closer to my personal genome the better. That said, I think that seeding planets such as Mars might be ok, as long as your certain your not destroying something already there. Mans colonizing of space should probably not be based on planetary colonization schemes any ways, gravity appears to play a critical role in embryonic development, and if centripetal acceleration is an effective substitute for gravity in this regard then smaller bodies with less or minimal Gravity might be best for building the necessary nurseries.
I personally would like to have my species be more significant then Panspermian ejecta bacteria. The colonization of the solar system will require the cooperation and support of the majority of people on earth. A tall order indeed, but if the people who contributed saw immediate and mutually beneficial rewards then it would not be as far fetched as it one might think. The beginning of building the largest public infrastructure in history would be best achieved by building flying space elevators that would not only reduce the cost of space flight in terms of Delta V but also become a series of platforms for international telecomunications, high speed intercontinental travel, and a staging area for rapid deployment of disaster relief supplies personnel and 15 minute insertion times for strikeforce security forces.
The necessity of a truly international agency capable of of administrating the use of the near space environment and satellite orbital control will be required.