, I had just put in 4 new B9EQV spark plugs the previous day. 

Ed;

Sorry to hear of your disappointing trip.  But, hey; s__t happens.  You did the right thing, of course.  When the engine isn’t running properly, you take the nearest airport.  It’s great that you and your plane got down just fine.

If it is the plugs, perhaps it’s possible that the seals jumped over the protruding plugs for a while until they became damaged enough for loss of compression?  Pulling a leading plug should tell the story on that. How did you choose the B9EQV?  Did you know of someone else using them? I’m running the B9EGV and they are fine.

Al