Here's another idea to approach the refinery. Instead of making it add BP (Which basically makes it UBP if you spam them, unless they're like repeaters), how about making it so it recovers lost BP faster. For example, building one refinery would double BP regen, and next would make it 75%, increasing multiplicatively for each one after.
This would make the refinery a tool for recovering from alien rushes faster, and making them a target for aliens to go for during their own rushes.