I do exactly that. I will likely never really know whether or not it was worth the cost, but I treat it like insurance. At Airventure, I visited both the Camguard and Aeroshell booths. Both feel there product is the greatest. Both agree that the Plus in Aeroshell is not the same formulation as Camguard.
FYI - I had been using Avblend until I had to replace my camshaft at 500 hrs due to corrosion on the lobes.