We did 2 full days at TDS, and 1.5 at Disneyland. But we skipped a number of attractions due to crazy waits and them being duplicates from North America. It’s more about experiencing the parks and their atmosphere, food, then trying to ride everything, especially rides we’ve done already.
Rides I feel I would need to experience to feel satisfied:
Hong Kong:
Mystic Manor
Grizzly
Shanghai:
Pirates
Tron (haven’t ridden)
Zootopia
Seven Dwarfs (haven’t ridden)
The rest is honestly gravy for me
But yeah, I could see doing 1 HKD, 2 Shanghai.
But might be able to swing 2 at both.