Take a look at the BSFC plot. Any assist you do will have to be paid back at (225g/kWh) / (.70 efficiency), which is about 320g/kWh on the electric portion. At first, that sounds terrible, but if you would otherwise be unable to stay below 3500RPM, I think it works out in your favor.
Consider an example where you're climbing a hill at 80% throttle. With assist, you'd have 1/4 of your power produced at 320g/kWh, and 3/4 at 235g/kWh, which works out to a total of 255g/kWh. You can see the points on the BSFC plot where you could do better by downshifting.
@Bikeracer: I bet you could P&G with even better results if you left the electric motor out of the picture.
@Formula: I haven't checked for open loop, but I don't see any signs that the ECU is worried about the lack of assist. However, it's your right foot and right hand that control where on the BSFC plot you fall, not the ECU. With assist or without, if you push the throttle pedal all the way to the floor, the throttle plate is wide open, and the ECU gets wasteful because it thinks you need power.
I try to keep my TPS gauge between 50 and 75 for acceleration. Note, that would result in lots of assist if it were enabled.
The only regen I do is regenerative braking. I prefer DWB, but on offramps and in traffic, you have to slow down faster than that. This regen braking is enough to keep my battery charged. As the weather gets warmer and regen braking works faster and across a wider RPM range, I'll end up with more juice than I need in the batteries, so I'll spend it at some point.