I doubt if that will really work, since those transactions will be accepted by your node as valid once included in a block.
Yes of course, but as I said, if enough of us reject those tx in the mempool, they will be forced to find direct routes to miners, making their spamming more difficult. It's about sending a msg.
But what if I allow a small 80 bytes data carrier size? That is the default right?
Runes use the exactly 80 bytes of data. (The OP_RETURN operator). If you put datacarriersize=0 in your conf file, any transaction that has OP_RETURN enabled will not be relayed by your node. So yes, if many nodes do it, it will be more difficult for the miners to learn about these transactions and to include them in blocks.