More power does not normally equal better mileage. The stock calibration is designed to reduce emissions and give reasonable performance. After that there is little bit of lea way that you can use to get better performance but that may not get better mileage.
It is also going to depend on your expectations and where you spend most of your time driving. If you spend most of the time on a Freeway or City driving.
Personally changing the elements is gong to be expensive an you are not going to achiever what you want. It is more for those for who power is the number 1 concern at the expense of the rest.
Assuming you changed the parts yourself and you knew how to phase/time the Elements properly changing the Elements would still mean sending your Fuel Injection Pump to shop where they would run it on a test stand and calibrate it. Then if you wanted more then stock fuel injected you would have to tell they what you wanted the pump calibrated to.
The ADLA on the fuel injection pump limits the amount of fuel when there is no turbocharger boost. Removing (or without removing you could simply see if the provided adjustment gives you some more pep) that removes the limitation but won't give better mileage but could give a pepper lower end.
On the MW fuel injection pumps there is a rack limiter that people re-adjust to get more fuel
I don't know about the emissions stuff like the EGR and any sort of Trap Oxidizer making a performance difference.
Turbocharger waste gate adjustment so that you get the Max boost from it.
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