Touchy subject! Someone once said: if you want strong horses, you must feed them! True! But over feeding a horse does not produce a race horse.

But lets look at it more technically. 

Your engine has a certain efficiency,which depends on temperature, burning pattern, and the likes. Not much you can improve there. The fuel injection can provide very good atomization of the fuel and perfect fuel/air ratios in all operating conditions. This is something (at least)! The bad news is that a fuel injection also provides more power, and by using the increased power you use more fuel, although more efficiently. Your driving habits play a big role. I would estimate the efficiency gain at about 10%, the power gain at about 25%, effectively resulting in a 15% increase in fuel if you use all the power. Note that this rarely happens, unless you are racing.

A big saving in fuel can be achieved by running the engine "lean" during part load or cruising conditions. You can simply reduce fuel at partial throttle. The increased engine temperature (lean mixtures burn hotter) can easily be absorbed, without danger of burning valves. You would have to adjust the ignition as well. This can be done with all Perfect Power injection systems.

Measure the engine AFR with a WIDE BAND (BOSCH, LSU4) sensor installed close to the branches. This allows you to judge how much you can lean the engine during cruising and how much power increase you can expect at full throttle. If you judge that you can better tune the engine, then look at a SMT6 or SMT7 piggy-back tuner to achieve this.

time for re-charging.