Elisabeth, it's scary how well you've nailed this aspect of Russian popular culture (and more), with its implicit lack of a distinct Russian soul. (soullessness?). I think Russia indeed had a soul pre-Revolution consisting of, among other things, sentimentality, stoicism, insecurity, etc. But at the risk of making 'the big statement', I think that soul was lost over seventy years of, well, soul-deadening communism. This is not easy to do, since this,'soul', however characterised, would have been formed by a huge population over a period of a millenium. Still, just as an individual may be said to have lost his soul, I think Russia did.
But your observations wonderfully confirmed what I have been thinking for years about Russia , not only in terms of culture, but in many other spheres of life as well, namely that Russia doesn't import well. The attempt at importing the French/European Enlightenment was a failure. Likewise , and disastrously, with German Marxism. Likewise now with Western capitalism. And for a long time now I have been cringing at Russian efforts to capture popular American culture. From early 20th century American jazz, Argentinian tango, original American 50's rock and roll (with Elvis wannabes that made you want to laugh and cry at the same time), through Madonna and Lady Gaga wannabes to present day black rappers. Even allowing for the considerable difficulty of effectively capturing the spirit of an original artist (let alone a foreign one), Russians somehow always seem to latch on to the superficial features of a foreign culture and the result is inevitably cringeworthy.
I think the prevalence of "poshlust", (though cheesiness, kitsch, and bathos are pretty accurate, too) represents a desperate attempt to fill at least a part of the void left, not only most recently by the fall of communism, but even more so, by the loss of much of the preexisting Russian 'soul', i.e. predating communism. Could we say now that blingy and 'chiksy'-filled tv and videos are the opiate of the masses?(even of some of the American masses?)