..Sounds like its almost a no-brainer decision, if there's a tax incentive that will cover most of the additional purchase price of the Energi (plug-in) version. Only thing you have to consider/think about, is if you can live with the loss of some space inside due to the larger batteries the Energi version has.
We have a 2013 Fusion hybrid, which has same basic hybrid drivetrain as the C-Max. When we bought it over a year ago, plug-in Energi versions of the Fusion hybrid were very difficult to find, almost non-existent at that time. Also, tax incentive wasn't as good or as easy to get as yours. Sooo, we went with the regular hybrid version. Our main reason for getting it was the ease of flat towing, anyway, not so much mileage. That (mileage) was just a very nice, added bonus.
Its been great, have absolutely no complaints. Mileage is unbelievable as already mentioned (I average 48-50 commuting to work and back every day). Its a blast to drive and really like the looks of it. And, you just cannot beat how simple and easy it is to flat tow. No fuses or battery to disconnect, no crazy procedure to go through with the tranny when hooking up, no stopping every few hours to go through another crazy procedure, none of that mess. Just hitch it up, put it in neutral and go.
It is also really, really nice to have at campgrounds and parks, since you can ride around almost totally silent (and emission free), without bothering other campers as much. Its almost like having a big, very comfortable golf cart to ride around in, haha. :)
As already said, you definitely do have to run a charge line for it when you wire up your tail lights, etc. for the vehicle. Very easy and cheap to do though, especially if you do it at the same time you're in there wiring up the tail lights, anyway.