Correction noted; you were speaking of the incursion/interception as being a non-event ... and I was speaking of the cops/pilot's view that this was, indeed, quite an event.
I think the feds darn well better keep an eye on 172's (figuratively), as one of them could load up with gasoline (as in the 727 gone missing in Africa) and figure out pretty quickly where the motorcade will be.
I realize the precautions taken, as I was part of a deal working with Fed agencies when a POTUS came to my building and I now know many of the diversionary things they do. I am also sure I do not know even more of what was done.
But: If you want to pop the prez, a little GA gas bomb moving fast and low could get close enough to at least scare everyone. If our uninformed pipeline-spotter, toodling around in a 172, could get that close, I'm sure a determined terrorist could do better.
I'm afraid we might become a little too complacent.