These have been great discussions. I don't want to prolong them for the sake of prolonging ... so two quick points.
bballman: You're indeed right that that book cites some examples similar to your infield example. When you stated "if a player makes a mental mistake, such as misjudging a flyball, then recovers in time to try to make a play on it, but makes a physical mistake, then it is an error." -- isn't that really what happened in scenario 2? Probably depends on what criteria you use to judge a "physical mistake".
BOF: While I agree that mental mistakes are tough to apply, when you state at the end, "Same thing for dropped balls in foul territory, you wish you could call them an error, because that’s what they are, just not in the way the game is scored." -- I have to respectfully disagree with you on that one.
That one is indeed an error.
10.12(a)The official scorer shall charge an error against any fielder:
(2) when such fielder muffs a foul fly to prolong the time at bat of a batter,
whether the batter subsequently reaches first base or is put out.
The fact that he's in foul territory doesn't affect the situation (unless with a runner at 3rd the outfielder purposely lets it drop to prevent the runner from tagging up and scoring.)