Baron Munchausen: If you're looking to be logical try hanging the base and ship construction techs off of a theoretical "Engineering" field.
Good idea - this could be supplemented by requiring a second theoretical field ("Minaturisation" in line with the comments above or "Large-Scale Construction") for higher levels of ship design.
Baron Munchausen: And please, please break up Stellar Manipulations already! It's been a catch-all for various almost unrelated techs for much too long.
I'd second..whoops..third this.
It would seem better suited as a prerequisite theoretical field.
aegisx: How do you counter that type of expansion other then being forced to follow the same path?
One option would be to add minimum population requirements (if possible) to key facilities (shipyards, resupply depots) and to have these increase with level (on the grounds that more advanced facilities require better infrastructure support even if they need less staff). That way, expanding empires either have to focus on building up one or two colonies to gain access to better facilities faster, or use older facilities on new colonies and upgrade when population permits.