1) It is inefficient, but it should be. And that's the point of this point. There should be better options. This point is about anchoring the fact that in no way it is possible to block spam, this option is always here and unstoppable.
2.) no, the value does not matter. Utxo has to be saved in utxo set if it is spendable. It can be an anchor output, so you can't prune it, that would break lightning for example.
3.) yes, keep it inefficient, but more efficient than the option that bloats the utxo set. Prunable outputs are better than bloating utxo set.
4.) spammers don't give a shit about their reputation, they wear it proudly. This doesn't work. They just have a different mindset and they don't care about being excluded from the true bitcoiner tribe.
6.) miners should not care about reputation, the point of pow is removing the need for reputation and replacing it with profit incentive. Also, the miners choose to reveal their identity, but they can choose to mine completely anonymously, removing any reputation costs.
For shareholder, the main reputation is if the operation is profitable. And that's a good thing.