What are the effects of upgrading Aqueducts/Pastures?
I realised I could just export my save and test this myself. The answer for anyone who needs it:
This will reset the building count to 0 (not replaced). The new building does not retain catnip effects. As upgrading destroys it is better to sell all your buildings to regain resources prior to upgrade.*
As you lose catnip effects don't forget to transfer more kittens to farming to pick up the slack.
*You may well go over your cap so do this carefully!