My take, and perhaps others who know more will correct me:


I think you are indeed reading too much into lens age.


Optical designs don't age nearly as fast as electronics. These are all modern lenses. Canon updates camera bodies regularly, but I wouldn't hold my breath for an update on a lens.


IMO, weight and cost are much more important factors in this decision than age and image quality.


As for a good general purpose low-light lens, for still subjects I suggest you consider the 24-105 f/4 IS. The IS makes it hand-holdable in lower light than the 24-70, and the longer focal length makes it (IMO) just as good a portrait lens (very subjective, I admit). Of course, if you plan to take pictures of rapidly moving things, the extra stop trumps IS.


Best of luck-


Jon.