The thing that seems to have a large impact on population is spawning dragons.

[Classic]

So this is my suggestion to increase pop. Everytime you want pop to increase by 60-120 (depending on how many zergs are logging in) I suggest you spawn dragons more often.

This seems to attract the right kind of bluebies to sustain a healthy server population at all times that dragons are spawning.

I notice nothing else ever has a major impact on population except this scenario.

Just a suggestion to help constructively increase server population.