There's many ways to reduce the "clutter."
1. You can turn them off per forum.
2. You can change the 5 threads that show to less, like 2.
Search for similar threads when users are creating new threads
Maximum results: 2
3. You can disable similar threads, but keep enhanced search enabled.
How do you turn them off for each forum? I searched but can't find it. I really think this option should be built into Xenforo