In my experience, really trying to be semantic ends up requiring gargantuan leaps of creativity trying to come up with semantic meaning for elements that are there purely for presentational reasons (wrapper classes, clearfixes, etc.)

That still wouldn't be semantic. Their only reason for existing is for layout. If html/css were semantic you could write all of your html first without thinking about style or layout and then go do the css after, but that's simply not possible today.