Does anyone know if you can steal techs that aren't normally tradable?
Generally if a Tech isn't tradeable, it also isn't able to be stolen either.
There are some techs that can be traded that can't be stolen (Scatter Blasters 1 and 2 (but not 3...) as well as all the Terror Drone techs from the Yor tech tree for example), but I can't think of a single tech that can't be traded, but can be stolen.
Losing the infrastructure does suck but OTOH it means you can often use the cheap effective Tidal Disruption invasion without adverse consequences.
The Invasion tactics are probably going to have to be rebalanced/costed for this reason. There is basically no risk to using some of them now (Mini Soldiers and Tidal Disruption, I'm looking at you...).
There will be nearly no reason not to use Tidal Disruption (if you have it) against the Yor, for instance. 90% of their buildings can't be used by the other Civs and would be destroyed anyway.