According to this answer there are two types of 〜ない adjectives, those that contain 無い (like 情けない, つまらない also falls here) and those that derive from archaic なう verb (like 危ない). For the first 無い type, how natural is it to negate such an adjective?
Google finds relatively few instances of, say, つまらなくない, some of which a not real negations but questions like "boring, isn't it?". However where are also cases like つまらなくない話 and I see how it might mean "not boring, but still less than interesting". However I can't quite comprehend what kind of person 情けなくない男 would be. In most (all?) cases there's an antonym to 〜ない adjective, so the utility of negation is questionable.
So, is negation of such 〜ない adjectives considered natural, or do you normally avoid it?