Science per turn doesn't get you to science victory; its a resource that moves you up the tech tree. Culture per turn doesn't get you to culture victory; its a resource that moves you up the civics tree. Tourism is the end mechanic of the culture victory, it doesn't add to your empire. Spaceports are the end mechanic of the science victory, it doesn't add to your empire.
Not a bad argument, I like it better with that idea in mind.
I still think they are far apart tho for several reasons. For example:
- There are a lot of more things to improve tourism than "spaceports", from buildings to policy cards, to terrain improvements, and so on. Thats because teh science victory counterpart uses those things for increasing science, the useful thing, not spaceport building.
- Several civs have big tourism bonuses. I just cant like those civs. No civ has "spaceport bonuses", they have science bonuses which makes them stronger.
- If having a tourism victory in mind, many games start planning it from the first city and city locations. In most cases you start very early to do things to improve your tourism, not culture, which again, beneifts your empire 0.
Im sure there are more. But you see, I like your argument, spaceport=tourism comparation is not a bad one, but not even close to be accurate. Spaceports is much more like a finishing touch of the science victory, and science the real improtant thing, than tourism vs culture.