Allow me to make a few corrections here. A person who is tall is not going to be more comfortable by purchasing an addtl seat...unless it is the seat directly in front of them and that seat is taken out. Sitting sideways, sticking ones legs over to the area beside them, is not more comfortable...believe me. I've tried it, dh has tried it and dd has tried it. You were just unlucky enough to get an inconsiderate person next to you. I have had perfectly 'normal' (oh, how I hate to use that word!!!) person sitting next to me and they encroached on my space. It's usually more about common courtesy than it is about size.
Also....those areas with addtl legroom?? Yeah, not just $10 addtl. That $10, for EBCI, gets you moved up in the line but does not get you the extra legroom seats, unless you are lucky enough to be among the first 10 or so people boarding...and assuming there are nomedical preboards, minors flying unattended or business class people.
You have to pay the huge fare for business class to be assured one of those seats..usually over $300 each way!!!