I understand that ... but if you don't do a good job on the pregnancy itself then what you have is a more tedious way to "buy" units. It won't be meaningful to the player. But I don't mean that pregnancy should take a LONG time. I think a little bit longer than PiC makes sense ... long enough to have a little bit of suspense and to affect gameplay but not enough that the player gets bored waiting.
The most important thing is to make every gameplay element "deep" and "complete". If you want pregnancy, really think about how to make it GOOD pregnancy and then do it that way. If you don't want to do it "good" don't include it at all. That will give you tight focus so the game really is good at the things it does.