Not necessarily. You may be able to make more power by increasing efficiency, but it will only be a small amount in these cars since they are already inherently efficient.
Making more power, say to the 130hp range and above, will be done usually at the expense of efficiency. The trade offs to produce more power are done without doing the other things that allow the highest efficiency levels to be obtained.
For example, to get the most power in a diesel, you lower the compression ratio so you can run the boost up and cram more air into the cylinder. More fuel is injected. You will, at the very least, incur more pumping losses. Additionally, a loss in compression ratio will mean that you lose efficiency as well. Why would you drop the compression ratio? Because the block will fail if you don't.
Trying to produce huge power from any engine, let alone a slow spinning diesel is an exercise in compromises, and if the goal is power, efficiency will be compromised. You can't get around the physics.
Cheers,
PH