Wow...that is sounds like a brutal trip. It sounds like AA has some process issues in the UK. Starting with the non-24-hr. reservation line, and continuing with rude service at the airport. The exit-row seat issue is sort of a tough one - I always book exit row myself, but if a flight gets canceled, it's a little much to *expect* a great seat assignment on the next (already full) plane. The empty-business-class scenario should have been handled differently (i.e., they should have probably given you one of those seats).
I probably would have hightailed it to Boston on the early flight (in whatever seat) and cut my losses, but that's JMHO.
jAAck brings up a good point about elite status (particularly Gold). Just ONE deep-discount round trip from the Midwest to Europe will earn about enough points to complete a Gold challenge. One trip in full-Y or higher, and you're Plat.
Four years ago, I was AA Platinum and picked up most of my tickets at a city ticket office in Schaumburg, IL (in the pre-e-ticket days). The agents there were VERY friendly and frequently would go out of their way to ensure a good seat assignment, best airfares, etc. Occasionally, they threw in a free upgrade or "forgot" to collect a change fee. They ENJOYED providing quality service, and probably did so for Golds almost as much as they did for Plats. Whenever I had a choice between UA and AA, AA got my business because it was so pleasant to deal with these employees.
One day I was waiting in line at the CTO behind another customer who was arguing with one of the agents (about what, I don't know...). After he walked away, the agent said to me "There's nothing that annoys me more than when people constantly remind us of their status, and EXPECT us to bend the rules." Probably the guy was trying to finagle a free upgrade, or maybe trying to get out of paying a fee - something he might have gotten with a different attitude. I guess the point of the whole story is that (1) the agent KNOWS what status we are without us throwing it in their face, and (2) elite status DOESN'T give us the right to act like a******s. If AA fails to deliver on a published benefit (preboarding, etc.), that's one thing - but I think sometimes we expect to be treated more special than we really are.
FWIW, AA is better than some... Prem Ex. status on UA simply elevates the level of courtesy from reptilian to sub-human. AA's Gold desk is, for the most part, actually NICE to people...