I think downvotes are required to an extent, but I do think that a warning should be given first. It gives people a chance to change and if people don't like the result of that discussion, then things will proceed. I don't think giveaways are purely spam, but there is a lot of posts with little to no changes between posts. I do think it could be seen in a way low effort as there are other things you can add to the post to make a little more unique.
As for self-votes, I don't self-vote. When i first joined Hive and didn't understand, I did but that was when my vote value was almost nothing. After learning about the system, I decided that it was self-voting my own content didn't make sense. It sounds more like gaming the system rather than seeing how others view your own content.