I used to do (2), before I did a recent India trip with my wife. I have been lucky all my life when it comes to having nice co-passengers, but this guy shattered my track record. He had the middle seat, and was willing to exchange it for the aisle (but not the window) seat. Among the things he did to me were wake me up every 30 mins on a 15 hr flight, drunkenly pour a drink on my pants and use my shirt as a napkin after a cutlery-less meal.
That's awful, but it doesn't seem related to this tactic. If you had booked two adjacent seats, he would have just ended up in the third, and you'd have the same problem.
YMMV (and I hope it does)!