Sure, let's stipulate everything you've said. But, we're having this discussion in the context of this thread - a thread with the title, "North Korea Will Listen, but Only to F-22s".
I believe the point the author is making - a point I'm neither endorsing nor refuting - is that a show of force is necessary. To that extent, the choice between a Raptor or a Predator is pretty stark - a Raptor projects force, a Predator doesn't - at least not until such a time when air defense capabilities are completely neutered and the US enjoys air dominance.
Put another way, a Predator projects force to goat herders in the Hindu Kush, and to terrorists in Range Rovers cruising Yemeni highways. But, the Predator project zero force to a conventional army that enjoys robust air defense capabilities.
Can they be an effective surveillance tool along the border? Sure. But they aren't sending any kind of message.