It could be that American myths are only as important as the ways that they are enacted. They may be internalized, true, but how are they "played out" in the cycle of eternal return where myth inhabits the social/lived realm?Discussing all the ways in which American myths and preconceptions shape our spirituality would require several thick and carefully referenced volumes. But there are a few recurring themes I've noted on various forums: as a partial answer to the Professor's question, I might offer a few talking points on some of them.
Many American Pagans have jettisoned the coven structure altogether, choosing to act as their own High Priests and Priestesses. Their spiritual development comes not through membership in a faith-based community but through their own individual efforts. Sometimes they radically reinterpret their lives to incorporate their new spiritual paths: more often they reinterpret various spiritual paths to suit their lives. This plays into our Protestant distaste for clerical hierarchies, our frontier/colonial emphasis on self-reliance and our immigrant love of self-reinvention. One's relationship to the Divine is preeminent, not one's relationship with our fellow worshippers or loyalty to a spiritual teacher.
Contrast this with the views cherished in many other traditions. In Hinduism one is expected to learn at the foot of a guru with an appropriate lineage. That guru is afforded a veneration which might make many Westerners very uncomfortable. A HPs or trance channeler who expected students to kiss hir feet and burn candles before hir picture would be scorned as a demagogue and wannabe cult leader. We give the Dalai Lama all sorts of humanitarian awards, but tap-dance around his claim of being the latest incarnation of Avalokitesvara. And while we have innumerable guidebooks for solitary practitioners, a Yoruba proverb reminds us that "a knife cannot carve its own handle."
The New Age and neo-Shamanic movements have created industries dedicated to repackaging indigenous movements for Americans. To be fair, this didn't necessarily start on our side of the Big Pond. H.P. Blavatsky adapted Hinduism to suit Victorian tastes. But then much of the American New Age is the bastard child of a coke-fueled gang bang between Madame Helena and various New Thought figures. (A long-suppressed film reputedly shows a double penetration scene featuring Norman Vincent Peale and Napoleon Hill... ). Given our status as a former colony, it's not surprising that we have internalized many colonialist ideas. It is not surprising that we may see other cultures primarily in terms of their usefulness, or that we wish to export our ideals (be they "Christianity" or "Democracy") to the world.
This is not to say that America's myths are entirely misguided or completely wrong. (Few myths are!) We have committed many sins in fulfilling our manifest destiny, and we have often failed to live up to our own standards. But the same fervent moralism that inspired the Puritans has driven many of our most ardent reformers. The culture which gave the world Jerry Falwell and Carrie Nation also produced Martin Luther King, Susan B. Anthony and Eugene V. Debs: it inspired both Glenn Beck and Noam Chomsky. While we should be aware of our shortcomings, let us not minimize our triumphs.