I work at the Salem processing facility sorting packes. Lots of misconceptions here. There is no such thing as routine inspection by USPS employees, with the possible exception of media mail. Under certain suspicious circumstances a package may be turned over to the Postal Inspectors, who are a law enforcement agency, but that is rare. There is also no difference in the processing of first class or priority packages, they all run together. It is true that the handwritten messages don't make a difference in processing, with the exception of live animals, but your carrier should be paying attention to them when they are delivered.
Mickey, first class and priority both go to Portland where they are flown out of the airport on UPS or FedEx aircraft. They are on the plane the same night that you drop the package off at the post office as long as you get it there for the posted last collection time.