Interestingly, the idea that John was influenced by 'Gnosticism' has now been abandoned by scholars, as our understanding of Hebrew mystical speculation has increased in the last 50-odd years, thanks to Christians actually listening to Hebrew scholars!
Having said that, from the standpoint of gnosis – rather than a narrow-perspective 'Gnostics' (a la Cerinthus, perhaps), then I can see that.
Do they not favour Paul at all?
I wasn't aware that John's Gnostic influence was abandoned by scholars, but I'm not surprised. To be quite honest, I never quite understood what other Gnostics saw in it. A lot of the supposed symbolism they drew out seemed like a stretch. That said, it's true that a lot of modern Gnostic sects, like the Mandaens and the Johannites, place an emphasis on the figure of John, so perhaps that has something to do with it.
Personally, I'm more of a Sethian. Despite my flirtations with Jung, I mostly try to stick to Sethian texts with a particular fondness for Zostrianos and the works of Zosimos. As such, I don't really use the Christian Bible at all, although I retain a lot of respect for some of the verses and the Sermon on the Mount from when I was Catholic.
As for Paul, some Gnostics do hold him in high regard. Marcion surely did, although I personally wouldn't consider Marcion a Gnostic. The Paulicians did, but, again, I wouldn't really consider them Gnostic, either. Many modern Gnostic Christians still view the Bible as essentially canon, unlike me, although their attitudes toward Paul specifically vary from person to person.
There might be some later Gnostic sects that placed special reverence on Paul. I'll admit that I've really only studied Sethianism, Valentinianism, Bogomilism, Catharism, Manichaeism, and Mandaeism with any seriousness, which are the main heavy-hitters in most discussions. I don't know very much about, say, the Borborites or the Audians, aside from their existence.
