Isn't the aero benefit only relevant at a maximal or near maximal effort? The fact that someone doing 14mph gets a greater time savings is only relevant if they are in a time trial, and their maximum effort is 14mph. But as soon as you are riding in a group your pace is set by the group and not your max effort. So no matter what kind of rider you are, if you want an additional edge when you are at maximal effort, than an aero frame might be one solution. But if you're not racing it's never going to provide much of a benefit...