Will these domed planets ever grow larger?

[Suicide Junkie]

Yes. In the same tech area, too.

After 3 levels of conditions improvement plants, you get 3 levels of value improvement plants.
After that, there are three levels of "Atmosphere Converter" facilities.
The higher tech ones work faster, taking only 20 turns intead of 30.

Once the atmosphere is converted, you can scrap the converter. The domes will be gone, and the space on the planet will go up 5x.