I'm still wondering why "mature content" has become a synonym for "sophomoric"...
It's not necessarily; I think the "Book of Vile Darkness" themed adventure in Dungeon was extremely well done, and one of my favorite modules in a long time. Plus, stuff like George RR Martin, Steven Erikson, Joe Abercrombie, Glen Cook and others certainly show that fantasy fans have a market for "mature content" that isn't sophomoric. The RPG side of fantasy publication hasn't really managed to execute their stuff quite as well, or at least as successfully.
That said, the original question is way too vague. Would I buy rules light mature products? Well,
what rules light mature products? Book of Vile Darkness was OK, although not exactly rules light. Green Ronin's Book of Fiends was actually much better, much
more mature... but also not exactly rules light. The Book of Erotic Fantasy is a bit of a joke 'round my neck of the woods; I wouldn't ever have considered anything like that to be a worthwhile addition to my RPG collection.
I certainly wouldn't automatically
not buy a rules light mature product... but honestly, I'd be skeptical of it, and I'm certainly not craving that kind of material in any way that I would ever go buy anything like that sight unseen just because it's rules light and mature, or whatever.