Thanks for the feedback!
Like a lot of the tools, features, processes, rules, etc. etc. etc., in forum-land, this new feature has pros and cons... and some aspects people think are pros, others may consider cons, and vice-versa.
We're keeping an eye on the way our members use this new "similar threads" tool. While there are cases where it can be more "problematic" when something is bumped (like a chicken for sale 10 years ago), there are TONS of great examples of helpful info and content that are bubbled-up, and are proving helpful.
Fortunately, BYC's content is more "evergreen" than most forums (vs. say, a tech site), for example: a tread about "how do I treat bumblefoot" 10 years ago is going to contain pretty much the same info as a bumblefoot thread from a week ago. We are seeing some really epic content from many years ago getting new-life!
All that said, we'll keep an eye on the trends, usage, and feedback, and make tweaks where we can (for example, removing BST threads) and where we can't (unfortunately there's no way to disable the feature by user).