I've heard of the same problem witht he "ancient precursor artefact" event that gives one races a mall, but exponentially increasing bonus. Crush them fast or they become unbeatable. IMO thatevent could be improved by:
1) limiting it to minor races
2) Capping the bonus (creating a funtional limit on how much you can learn from 1 artefact).
as far as the terraformer goes, it might be better if once again the bonus was always focused on a minor race or sparesly populated area. This would encourage a "gold rush" where every race tries to capture as many of the new worlds as possible.
