F3G,
Have read this thread with interest as I have just been on the receiving end of a similar situation (with another airline) in the past day/night. As you infer, the worst part of the experience is the feeling of helplessness when no one appears to be doing anything to put matters right. This is especially frustrating when the airline is constantly telling you how you are a "top100 customer" etc etc.
The reality however, is that a short, polite note to the senior management is likely to have far more effect than trying to go legal, particularly with consequential damages which, in this country are almost impossible to achieve for this type of issue.
For what it's worth, it encourages me that for every rude, uncaring, inept, inefficient, witless jobsworth that you might just meet at a US airport check-in desk, there is someone like VS-LHRCSA who, if written to properly, will make it all better again
Strake (who yesterday, was seething with anger, bristling with rage and calling into question the parentage of the management of a certain airline but is now calm....very calm.....)