I'm not a terror star fan, but restricting them is a silly idea. It'd be like preventing 'good' civs from using the best weapons, because they kill too many people. Good civs have no problems slaughtering the entire population of a planet in ground combat, after all.
Dyson spheres are an absurd idea, since anyone with the materials technology to build one wouldn't need one anymore. Ringworlds or Orbitals are a much better idea, since they don't require several systems-worth of resources, excellent timing to prevent the star being destabilised, or beyond-insane materials strength. Actually, throwing the odd Orbital into a system would be an interesting way to get a few more 'tiles' to build things on - although they'd cost absolutely ridiculous amounts of resources. Maybe a new, very high-tech version of starbases? I imagine this is what they're doing with terror stars, since they're just movable, armed starbases. The 'nice-guy' option would be to make such a structure habitable.
