The B14 is a great bike. I would say the obvious upgrade would be to throw some race wheels on there, but that can be pricey. I think if you were looking to get the bike to the next level, upgrading your shifters/rear derailleur would be a good bet for sure.
No need to update the shifters or the whole rear derailleur, maybe upgrade the derailleur pullyes to dura ace pulleys.
The frame is solid and comes with a decent aero bar (faster aerobars are out there, but more expensive and/or less adjustable). I would first make sure you fit is good by riding and adjusting for a while, then maybe find a faster aero bar that would fit your position.
Cheapest would be to get the Felt Torhans frame bottle and use it for spares if you are not running a frame bottle, since the torhans improves the drag of the B14. If you can mount a torhans 30 close to the head tube, that is another solid upgrade.
Next bet is a set a race wheels (with fast tires and tubes to match), just search the classifieds for used zipps or heds. Really only need a fast front wheel and use a wheel cover for the back wheel.