Those are all fine opinions, and I'm starting to understand your point with all of this, but they are still just opinions derived from assumptions. None of us know what the guy was thinking. But I totally get your point about why he would he even care to argue about a refueling stop if he intended to jump early in the trip. That element has always made me wonder what he was thinking during all of that. Would LA and SF also have flown down V-23?
To say there is no evidence for a Portland DZ is obvious...but there is no evidence for ANY particular DZ.
One thing I've learned from getting close to Mac over the past year is how intricately he planned certain things yet completely brain farted on others. I get that sense from Cooper at times. Mac and Cooper aren't exact analogs but it appears that they were both winging a good bit of their hijacking.
I do have a hard time with your theory that Cooper didn't have any idea of where he wanted to jump. All of the copycats at least had a rough estimation of where they wanted to jump. They all were planning to jump near where they felt they'd be safe. Mac was planning to jump within an hour (driving time) of Detroit, Hahneman jumped into Honduras, LaPoint was living in Denver at the time and jumped 90 miles north of Denver, and of course Heady and McCoy were jumping very close to their homes.
As for the Mexico thing, my belief is that Cooper did a little research and saw that the max range of a 727-100 was about 2400 miles and, incidentally, Mexico City is almost exactly 2400 miles from Seattle. Seems to me he wanted the plane to be in flight (without him still in it) for the maximum amount of time, so he picked Mexico City. Of course he seems to later say "anywhere in Mexico", but the point stands.