but if all you vote is only people of similar stake that also give you a vote back you're not really participating in "curation"
I am not surprised to see tha abuse and I agree that this is not a good thing.
On the other hand, my own vote distribution also concentrates on a couple of users I interact with.
On one side, as you already mentioned, this is normal. It are the Hivers with who you have something in common. And it is surely no vote trading.
On the other hand it's also because I often use the following feed to curate. All other feeds give me too much junk which makes it more time consuming to use. But this is bad for vote diversity.
I'm working with Eco on a tool with which you can filter the blogs stream to customize it. Did you read it?
Eco is developing a MVP to see if there is interest in such a tool.