I think that may be conflating cause and effect. I'd argue a manned trip to Mars is a focus of pop culture because it resonates strongly with so many. The drive to explore has always been etched into a portion of humanity. For many(myself included) Mars stands as the currently realistic pinnacle of exploration for humanity. Along with accessibility of understanding the accomplishment you end up with our current Martian fascination.
>I don't want to be labeled a cynic, but do the benefits of sending humans to Mars outweigh the costs?
With anything as expensive and complex as a manned mission to mars, we honestly can never know until we try. It's impossible to predict what fruits, if any, it would bear for humanity. That's the nature of exploration and discovery. For all we know there's some infeasible to overcome barrier that makes the task of manned travel to Mars impossible.
Due to the intractable nature of quantifying the value of manned Mars missions I think the reasoning for doing so falls to a far more base human condition than a positive cost benefit analysis. On a personal level the desire for continued human exploration is hard to explain to those who don't possess it. There's an intensely disquieting internal sensation that comes with feeling stagnation at the bounds of human capability. It's not dissimilar to the urge for preservation of the Earth for future generations, or to rid the world of undue suffering. These drives, like exploration, aren't built on entirely pragmatic foundations. They can and do often fail to justify themselves on purely practical terms.
Just for clarity, my response isn't made with the purpose of persuasion. It's to help convey my entirely subjective view of things and perhaps illuminate the thinking behind some proponents for space exploration.