There are lots of similar ideas here to another thread that I went through the same principles of using the globe for the career and as said you create a park at your chosen starting location with them being easier or harder depending on where you start with different bonuses and restrictions (similar to how XCOM works if anyone has played that).
Then over time you get offers around the globe to open up new parks, each area bringing different challenges such as: weather/climate conditions, building restrictions, land restrictions, rival parks already there etc etc.
This is then how you progress your theme park empire. The AI parks are similar to that as what Theme hospital does. Your park will compete for local and world records, awards and thus this affects both your overall company reputation thus all your parks and also your local park reputation.
It means you have to think about your benefits not just locally but globally. Do you want to build the worlds tallest coaster at park Y when you already have that record in park D. Yes you would get great reputation locally and boost there, but it will cost of course to build and your taking your own record from another park and thus a negative effect there. But then it is established so is that loss not as great as the gain, let the player decide etc.
So yeah you have the competition, the global link, the reputation systems, the progression etc. You could even have something with a bit of a random generator where you are say on park 7 when suddenly you have issues with your 2nd park and you now have to go back to that like a "critical mission" where say a natural disaster (earth quake in land or tsunami on a coastal map) means that your park is closed and seriously damaged and you now have to work through your options on how to re-open it or even abandon the park due to the expected costs. It will mean that your reputation may take a hit globaly if you don't get it up and running within 'X' years of the incident, however financially the loss of income from the reputation is better for you than the cost of rebuilding.
With that the player can decide if they are going to be a Tycoon master or someone who is more environmentally minded and want to give the public the joy of theme park. It may be that the board of directors have stipulated that you resolve the matter or that the local governing body has stated that it has to be repaired and provides a grant to help get it running again.
Then you add in the other career discussion about the land geometry and buying parcels of land with their bonus and negative effects accordingly so that each region you build could turn out 10 times different just in the space you are able to use and that will always affect how you park ends up. Let alone then of course completing different scenery, coasters etc each play through. Finally add back in the AI affecting how you tackle those maps each time as well, the random order that you do it in, your starting location.
The career will remain very fresh for years because of this. It could be there are 6 starting locations (1 in each continent not including Antarctica because of course being able to run a theme park there is not really viable). And then each of these continents would have 4 locations on them for the ability to build theme parks. So overall you are talking about 23+1 locations on the globe. It means then later as the game progresses more areas could be added to different continents. You could end up with say 36 locations on the globe for instance. That is 36 unique places which all have 10+ different variations of building your park by buying different parcels of land in that area. So in theoretical you would have hundreds if not thousands of variants of parks just in shape and geography alone without even having to get the sculpting tool out.
I think honestly this should have been the starting point for the career and really making it "Planet Coaster".