What about adding tangible incentives for running a full node, like lower transaction fees? Does this go against Bitcoin's creed or functionality?
You couldn't set lower transaction fees for full nodes because miners typically include whichever transactions have the highest fees in blocks first.
Regardless, I think that trustlessness is an important enough benefit in itself - if a person cares about independently verifying that the consensus rules are being followed, they will have to run a full node.
I also think that having a direct benefit for running a full node - like a payment - would result in huge node farms rather than people using the nodes as their own wallet.