I just bought a used 2013 volt with 140k miles for 8k (I get it, I couldn't wait any longer either!) So far it's the coolest car that I have ever owned. I'm getting about 45-48 miles off the battery on my commute 82 mile commute with combined economy of about 85mpg. I put it in gas mode (hold mode) for the hilly parts on the freeway, and battery around town (I get more off the battery than the 35 miles it's rated for due to regen I guess). If I put it in sport mode and punch it the acceleration is much better than a prius although nothing like a sports car and it feels like it will coast for days. The interior is great, all leather, comfortable seats (although not motorized), the bose factory sound is decent for stock stereo. The only thing it lacks from the new model is the longer EV range and updated tech (I'd probably be getting 60+ on the new volt off the battery) and android auto / apple car play.
Not sure what you mean about "the fuel efficiency vs a consistently charged Prius is simply not as good." You mean plug in charge or always charging? You can put the volt in mountain mode to have the engine charge the battery when gas mode, but it's less efficient than simple letting the volt do it's thing in gas mode. Converting gas to battery storage is never as efficient as just using the power. Or did you mean plug in charge every night because the volt does that too? The new volt has more than double the EV range of the prius prime as it is also a plug in hybrid. Also the Volt has a liquid cooled battery like the bolt and teslas, and the prius battery is just air cooled. Chevy did really well on their battery tech. The price difference between the 2 cars isn't was much as you would think either (you get a larger federal tax credit for the volt)
Final Scoring, Performance Data, and Complete Specs
Certainly both car's have their place, the volt only seats 4 people, although I wouldn't want to be in a prius with 5 people in it for very long anyways.
I plan to sell the used volt when my tesla becomes available. Hopefully without too much of a loss since most of it's depreciation has already hit.
1 gallon of gas in a volt will get you 53 miles ev (by specification) + 42 miles from the gas so that 95 miles for the first gallon of gas.
1 gallon of gas in the prius prime will get you 25 miles ev + 53 miles from the gas which is only 78 miles...
2 gallons of gas before a charge = 137 miles volt, 131 prius
So if your commute is over 137 miles without charging you will soon start saving gas with the prius over the 2017 volt. Of course you can probably get better range off either vehicle since I'm getting closer to 45 ev miles off my 2013 volt which is only rated for 35 miles of range. I'm consuming less than 1 gallon of gas per day on my 82 mile commute. MPG on the 2013 is only 36 miles per gallon in gas mode. By the math I should be using just over 1 gallon of gas, but that is not the case