How are change addresses treated differently by Bitcoin Core? I understand the reasons for wanting to use new change address for each transaction, but am unsure as to how they are treated by the Bitcoin core client. 


Is the address deleted as soon as the funds it received as change are spent?
The client probably doesn't watch for any further sends to these addresses, right?
Is the address deleted as soon as the funds it received as change are spent? 


No, the change address is not deleted but it is stored as another of your key pairs of your wallet. Bassically when you make a transaction with 1 BTC spending only 0.7 the remaining 0.3 BTC is send to new address that is stored inside the client (current account) waiting for new transaction from operating "main" address to occur. 

Try yourself list your addresses (after you spend input on one of your change addreses) with command: listaddressgroupings


The client probably doesn't watch for any further sends to these addresses, right?


No, the client updates the balance on all keys inside the client. The change address can receive and sends BTC. The remaining funds will be updated as part of the main bitcoin address.

For more information see: Change on Bitcoin wiki