- Apart from forwarding transactions, is there any value in my running the code?
Yes. You are enforcing the consensus rules.
- Your node will reject any blocks that don't follow the consensus rules.
- Your node will reject any transactions that don't follow the consensus rules.
- Your node will reject connections from peers that send too many invalid blocks or invalid transactions
In this way your node maintains the global database of transaction history and prevents miners from changing the consensus rules without the consensus of the users (including you).
- If not, is there a way to disable mining and just do transaction forwarding?
The Bitcoin Core node does not do any mining anymore. You will never solve a block, because you are not mining.