With limited regen, a plug-in could be the solution. My LaCrosse seems to go into regen mode every time my foot leaves the accelerator, unless I coast in neutral. The touch screen and DIC both have an optional display that shows current flow - toward the wheels when the generator's engaged, and toward the batteries in regen. My DIC looks like this one; touchscreen is larger:
I see the biggest benefit of the eAssist system on the highway, where it keeps me in TC lockup. I can both hear and feel (slightly) the generator kick in at speed.
I'm sure it helps at lower speed, as well, but that car is so heavy and takes quite a bit of effort to motivate it from a dead stop. The DIC instant mpg readout is dismal in those circumstances, but it would probably be a fair bit worse without the eAssist.