I was thinking the same thing Saturday on the way home from the CVA Convention. Mine have not been adjusted in 10,000 miles and now seem quieter than they used to be.Only thing I can think of that woud tighten them up is valve seat recession from unleaded fuel. I used to use a lead additive till around 5,000 miles ago but stoped after an internet debate convinced me it was not needed.
Will report back after I adjust them