The belief that the material world is evil is very much in tune with modern "spirituality," particularly if ritual sexual practice replaces celibacy in the ascetic. The rationale for that approach is that sex is a transcendent spiritual act which, correctly used, is integral to overcoming the material.
This is the essence of the heresy propounded in Holy Blood, Holy Grail and stolen so shamelessly by Dan Brown. Its appeal is clearly demonstrated by the publishing success of the original, and of the plagiarist DaVinci Code. It's no sillier than the belief that anything created by God could be intrinsically evil, or that God would allow the material world to be created by an evil demiurge (among many Gnostic variations.)
If you want to object that this is not "original" Gnosticism, I would say that historically I'm not sure that's true; there are, as you observe, many variations of this heresy. But even if I stipulate to the hypothetical that it isn't originalist Gnosticism, it is very much in keeping with the modern, buffet approach to "spirituality," maintaining that materialism is evil -- except for the fun parts.
I have no doubt that a lot of moderns are attracted to what they think the Gnostics believed.
I just sincerely doubt many of those who do have much of any idea of what the Gnostics really did believe. They project modern viewpoints into the past and think, “They were just like me!”
This is much like modern “indigenous peoples” who romanticize their ancestors. I suspect any modern Indian or Hawaiian who actually got to meet his Iroquois, Comanche or Polynesian forebears would be appalled.
Just as I would be by my Viking and Irish ancestors.
Anyway, I stand by my assertion that upper-class twits living a 21st century life of luxury and sexual indulgence that only kings enjoyed in the 3rd century have little in common with Gnostics who believed the path to salvation was absolute poverty and celibacy.
These moderns may talk a good game about living a simpler life, but with perhaps rare exceptions they always want someone else to live that life.