I wouldnt be so sure about an African Colonial Empire, would just take too long to research the techs to get that far, while reclaiming the America's would be full of wars and other good stuff. And besides, you already start out with a stepping stone into the America's... Cuba.
Yes, you're definitely right about that. The techs would be especially difficult given Spain's low literacy relative to places like France and the UK. So I think maybe I'll just pursue a little of both, should I decide on Spain. The other question is whether I let the Carlists win or not.