genejockey 

Lighter will make very little difference on the flat, and only a very modest difference on a climb.

More aggressive will make more of a difference than a lighter bike, but if it's more aggressive at the expense of your ability to put down power, you may lose more than you gain. If you're riding mostly with your hands on the hoods, you can get more aerodynamic by riding in the drops, or even better aero hoods. But this presupposes you're riding mostly on the hoods. If you're riding on the curve or the ramp behind the hoods, or even worse, on the tops, then just going to riding on the hoods will make a difference. If your bike is set up so that you can ride comfortably in the drops, then aero hoods should be doable. It's mostly a matter of practice. If you can't ride comfortably in the drops, though, then lowering the bar won't do you any good. But if you can ride really comfortably in the drops while pedaling and putting out power, you MIGHT think about lowering the bar. But if you do and you find the hoods are too low or far away, you won't use them and you won't gain any aerodynamic advantage.

WRT the tires, it's not so much the weight of the tires that's the issue as it is the suppleness or lack thereof. Something better than the Marathons will be faster.

Biggest thing, though, is the motor. Ride more, ride longer, ride harder. Practice riding as aero as you can for as long as you can.