--The change in the marketing strategy for "B" films that took as much advantage of the declining power of the Production Code as possible;
--The escalating existence of maladjusted and downright psychotic characters in 50s noir and exploitation films, which led inexorably to the subject of sex;
--The beginning of media fascination with the bizarre and the psychoexotic in the underbelly of American society, and the institutionalizing of a hedonistic youth culture that required more and more "kicks." By the early 60s, all bets are off and the grindhouse circuit is a sleazy profit center unto itself.
What is intriguing, though, is that there is an attempt to create an "avant" out of all this. It's mostly a feeble attempt, to be sure, but the results are sufficiently strange and unusual that it deserves some kind of "culling out" in order to see how it contributed to the broader change that exploded into a "new Hollywood" in the second half of the sixties.
In its own context (1959-66 or so) we probably would be well served to put some of the films that come close to being "roughies" but don't fully qualify according to the specific definition. More "mainstream" filmmaking was also trying to come to grips with nudity and sex in this time frame--as we've seen in the French noir series, these issues are already coming into play in the late 50s. Putting some of the more "mainstream" films next to out-and-out, fully-blown "roughies" (a pun I am REALLY going to leave alone...) is a good way to gauge how this content is being handled across the spectrum of film production at that point in time.
And I think in order to get anyone to put on such a festival under today's conditions, a little "tempering" is probably a good idea. But I think there is something startling there, as Richard suggests, that's caused by a break in the paradigm of filmmaking (the early talkie analogy is interesting in that regard) and we would be well served to try to put our finger on that pulse (if possible).