Honshu, you can actually get food on a third planet by researching good Xeno Ethics and building the Gaea theory galactic achievement, and you also get the Church of Valor for another 25% soldiering bonus, which probably makes good the better choice of alignment to go with when playing Thalans.
Netherless, I'm just not feeling what the race's strength is suppose to be. They are super builders who have nothing to build for a long time. They can colonize quickly but then wait around while being bullied by their neighbors hoping to get their tech up. And when they tech up their special racial techs seem mostly random and meant more to minimize their weaknesses than work together together to give them a significant edge anywhere. Galactic achievements aside, none of their standard complement of improvements seems any better than what can get off a standard tech tree.
I mean, compare the Thalan to the Drath for example. Both races have penalties to population and weapon bonuses in their tech tree. The Drath's tech tree though works very synergistically with their super ability. They can manipulate people into going to war, and then profit of the same wars. They may repopulate slowly, but are also have some of the best soldiering bonuses in the game, and they aren't working under the handicap of not being able to build farms.
As mentioned above, I guess you can go always use the terror star on the galaxy, but I don't see them being any better at this then any other race, especially since speed bonuses don't apply to terror stars.
And actually the same issue of not having a perceivable strength goes for the Yor as well. The other races may need some small tweaking but it's sort of clear what they are good at, which should apply to the Thalans as well (I'm not counting the Altarians as they really don't even have an individual tech tree yet outside of xeno ethics).
Anyway, I think the concept of the Thalans are pretty cool, especially their ethics tech tree. However, I don't see them as really being that competitive with the other races in the game regardless of what your playing style happens to be.