Other than a bit more insight on the impacts on human healthy from long term spaceflight.. What are the major scientific insights or developments made thanks to the ISS?
With Apollo there are quite a few, but with the ISS I can't think of anything
But the ISS should be considered a manned instrument bus. Consider OCO-3, a gimballed observer on the exterior of the ISS. It has revolutionized our understanding of global carbon cycles, and local carbon sink/sources.
There are numerous such missions that benefit from a common, well supported platform to operate from.
The next one should be robotic though.
https://en.m.wikipedia.org/wiki/Orbiting_Carbon_Observatory_...
We are essentially shipping up an instrument only, rather than the instrument + all the supporting equipment.
For a datacenter analogy, it's like adding a HD to a server, rather than buying a new server for more storage.
It could run from a sat, but then we'd have much fewer missions we could fly.