Spore was great, but there were things we wanted from it we didn't get, so people have worked to make spiritual successors. They either start at the beginning (cell stage) and get bogged down in feature creep, or they start with the part most people enjoy (creature stage) and it becomes mostly a clone with less impressive features.
When it was coming out, I was saying that maybe trying to do everything in one game was the wrong idea. Not that, in the end, they would all link together, but dividing the attention was the problem. That they needed to focus on one stage at a time, and make that stage, on its own, a full, complete, and fun to play game. Then, you could set it up so it could pull assets from earlier stages, and pass them to the next.
I would start with tribal, simply because it was the least fun stage. it was an afterthought. You couldn't customize anything other than a basic outfit. The gameplay was still "kill or befriend" but they tried to make it "tricky" by having to click the right sequence... like a Simon game where you don't have all the buttons at first.
I would remake that stage as its own standalone game, knowing full well that it would have a creature stage before it and a civilization stage after it (perhaps a town where agriculture mattered more than vehicles... farming was left completely out).
We start with humans. Boring, standard, familiar. Remake the tribal stage using humans. Then start fixing things: same model, all look the same. We need options for gender differences. Clothing differences. Members whose job it is to craft things. Customizable weapons, instruments, huts, village layouts.
Once it is up to a playable, fun game... swap out the humans. Put in the most non-human species you can come up with. Eridians. Heptapods. Birrin. Puppeteers. Flying creatures. Swimming creatures. Tall, short, fast, slow, with hands, without hands, with lots of hands, tentacles, lots of feet, no feet. Then play it again. What features need to be changed or expanded to work with this new species? Do it again with a third species. Then a fourth. Make it feel natural for whatever species you put in there. If it looks good for one, but looks weird for another, fix it to switch between them or be universal (why is a species that picks things up with its mouth making the same tools as creature with hands?). A tribal game that can work for any species you add into it. If you do that, then it will be ready for when custom species are included in an earlier stage.
And with all the variation, you now know how you will need to design the civilization stage to address all of these features. It won't feel tacked on, shoved in, playing simon just to get "aggressive, friendly, or balanced" status.
Create a civilization in the middle, then work your way out one game at a time. Make a game that can tie to all the other games, but also stands on its own two, three, four, or whatever, feet.
