This is a good point, and illustrates that a hybrid "best fit" is one where it has enough just enough power both to accelerate and to handle things like hill climbs etc. without having to wind out to an inefficient RPM, then it could allow the motor to provide extra "punch" if necessary. If oyu are regularly acclerating with tons of pedal pressure to get the acceleration you need, your fuel efficiency may actually slightly benefit with a more powerful engine, or see the same FE with more power in reserve.

I've been thinking of some ways I could do this myself, as the hilly commute in my area has proven quite taxing for the small engine once the battery pack runs out. What would probably be ideal for you for more power without much FE hit would be a turbocharger of some sort, to imrpove the pick-up in the 2000-2600rpm efficiency sweet spot. I've read of a few people who installed turbochargers in their Honda Insights, but that might be more difficult given the crowded engine-bay. There's also not going to be any commercial turnkey product -- a HCH-1 turbo woudl need to be home-made.

Another project you can see here involves manual control of the electric motor, I wish soething like this were available on the Civic -- it might then be possible to accelerate using the electric motor on demand rather than waiting for the system to "Decide" it needs extra power. Both performance and fuel eocnomy could be improved by more intelligent use of the battery pack.

Other possiblities may involve improving aerodynamics -- while this would not increase peak horsepower, you would be running with less load at highway speeds, and thus have more in reserve.