I have two B17's and a third backordered.The two I've broken in have never been in the rain without me on it. The first one has only needed a 1/2 turn tightening after 500 miles. The second one has needed 3, 1/2 turn tightenings as it broke in. I have swapped the seats around on my bikes and it was the seat itself and not the bike that was the variable. One thing I did notice was that as they broke in was that on my road bike I would slowly lower the nose as they broke in but on the hybrid the nose angle remained constant.
As far as throwing the spanner away, Brooks has been making seats for a long time. If they never required adjusting they wouldn't make it adjustable. I do doubt that they'll need to be loosened.
+1 on a little proofhide goes a long way.