[RuBBeR]

Travian has a very wide playerbase, this is because a lot less activity is needed to do ok/well, and the gameplay is much more appealing to the "not hardcore" player. So proberly only about 20% of their playerbase might be interested in playing planetarion. So advertising their would proberly be quite costly and you proberly won't get much in return for it.

That being said, their are proberly more games out their with players who might be interested in Planetarion, but the big problem indeed is how to reach them, because I dont think PA lookalike games will want PA adds on their site stealing their members.