best bang for your buck will be clip-on aerobars and forward seatpost. The geometry does not just save your legs, it is also more aerodynamic, and if you train in that position you should produce almost as much power as the other setup, with a bigger aero benefit from the difference. Yes there is an advantage, yes you should get aerobars and to shift just put your hand to the shifters. I would not redo your cables, no it would not be that worth it. if it is a technical course with a lot of shifting you would probably be on the brakes anyways. otherwise, choose your gear, and ride it until you need to shift.