I would like to start a discussion about this.
Back in GalCiv II I used to make plenty of multi purpose planets. More or less depending on several factors such as what race I played. I.E the Iconians were good at making general purpose planets.
Now, thanks in part to the new population based economy and the per colony Production wheel, I seem to be doing ONLY ultra specialized planets. It simply seems more cost effective.
It is hard to tell how that would play out in the long term though, as the need for flexibility might overcome the need for optimization on a larger empire.