If all OP cares about is improving aerodynamics to attain higher average speeds, the cheapest way to do that is clip-on aero bars on his current bike. Once you dial in your positioning on those, you'd notice a real improvement in your speed for a given effort. Just go out on your current bike, start hammering in the drops, and then put your forearms on the tops (if you're comfortable with that) to mimic the aerobar position. With the same effort, you'll notice your speed climbing immediately from tucking your arms in to your body and flattening your back. Fun to play with that stuff and see how much of a difference it makes. IMO the aero frame isn't worth it for you, but a newer bike, maybe a nice mid-range carbon frame with 105 5800, is within your price range and would give you better shifting and a nicer ride.