This relates to your concerns only remotely, but as I was just reading Hobsbawm's preface to the volume which introduced invented traditions, I was wondering: what distinguishes invented from non-invented traditions? (And, to wit, some traditions are NOT invented, though I must say that from the inflationary use of the notion "invented tradition" in the kind of media I read you'd get the impression that tradition itself is inherently invented.)

Does common memory play a part in this?

More to your question, your idea seems to presuppose that one defines group identities either through tradition (invented or not) or through contrast with others. But what about utopia, future, promise? Should the quite pervasive self-understanding of Northern America as the land of the free etc. not be considered here? Sure, this utopian myth also depends on contrasting yourself with others, but perhaps the utopian aspect is more important than the contrastive one - just thinking.

(Hey, what about some of these superb footnote fields in comments? They are wonderful, by the way. The footnote gadgets, I mean.)

I'm not at all sure if I really got your point, but I'll throw in my two cents anyway. My recent visit to the USA -- I was in Las Vega$ for one week (and yes, I was in THE show of Siegfried&Roy when the tiger attacked Roy) -- resulted in some thoughts which seem to go with yours. What astonished me was the ever-present celebration of the US, the flag, and the constitution. Even the generators inside the Hoover-dam are decorated with flags like they were birthday-cakes, or July 4th cakes. On the big billboard-screens, which are scattered all over the strip, every ten minutes or so a US-flag is to be seen flapping in the wind, and a text-overlay says: God bless America. Even showstars (in this case Penn&Teller) reflect on the flag and the constitution on stage during their show. All this becomes quite annoying to the european visitor after a short time (at least to me). [US-friends told me that all this sprang up after September 11.]
On the other hand whole Las Vega$ is a celebration of "good ol' Europe" -- the majority of the huge hotels are european-themed: There's the "Paris" (with a gigantic replica of the Eiffel-tower), the "Monte Carlo", the "Venetian", "Caesar's Palace", the "Bellagio" (resembling a resort at Lake Como, Italy), the "Excalibur", the "Aladdin", the "Luxor" (the last two are not european-themed, but old-world, too) and so on. There is an Asia-themed hotel ("Mandalay Bay") and one South-Sea-themed ("Mirage"), but interestingly enough no American-Indian styled one. Vega$ itself is only about one-hundred years old, but (on the surface) it tries to emulate all kind of history which dates back for centuries, in the case of the "Luxor" even milleniums. But everything is hollow, not only in a metaphorical sense, but literally. If you touch the statues of Julius Caesar or the enormous egyptian-style obelisks, you find that they're made of plastic, and indeed are hollow. If you enter the hotels you find that it's all about slot-machines (ok, this is Vega$, I know), food, entertainment and costly boutiques ... almost exclusively displaying european brands like 'Armani' and so on. Europe is THE metaphor for history and luxury. But everything is facade, nothing points to a deeper sense of history or even to a cosmopolitan lifestyle. In all those grand hotels (5000+ beds, several theaters, innumerable restaurants and shops) you can't find a bookshop. And the only newspapers you can buy in the whole town are the 'Los Angeles Times', the 'Las Vegas Review', and 'USA Today' -- there's no international newspaper, not even the 'Washington Post' on sale.
Now you may say, Vega$ isn't the US. Agreed, but the majority of the tourists and visitors are US-citizens and they like the town big time. (I am judging this by conversations I led and heard.) They're completely overwhelmed by it and there's not the tiniest fraction of dislike or even criticism 'cause of the ubiquitous hollowness and lack of meaning.
Are all those points born out of my european snobism and arrogance? Honestly, I don't know.

P.S.: There are pleasant points, too. E.g. everyone is friendly -- now you say that's only on the surface. But hell, I can't touch more than the surface of someone who rides with me on the city-bus, and whom I'll never see again in my life. And the bus-rides in Las Vegas are just great; everyone is cheering and joking and interacting with the bus-driver -- it's a big show, too, but a good one.

/end of rant.
--zeph