I wouldn't write off the importance of this story so easily - this is quite important if only for it's timing, what with a possible Tory govt. Without the special relationship, what exactly are the positives of us keeping Europe at arms length? No-one has thought Britain can go it alone since we pulled out from Aden. So if the FAC is saying this, and they're a somewhat influential group, it's showing that the idea of Britain having a viable future as America's partner is quickly dying.
Now, whether or not that idea was very viable in the first place is another matter, but there is no denying that it has been quite an important idea in British politics for some time. The Tories voting in favour of this on the FAC know this and know that the special relationship, even in words more than deeds, is the only thing stopping the British foreign policy establishment throwing its weight fully behind the European project - yet they still voted for this.
I think you're right that substantially this isn't new, but often the really important moments aren't when the reality changes but when people finally begin to admit things have changed.