2007 vs. 2008 model

Are they otherwise identical cars?

Your avatar shows what looks like a Touring Edition (16" wheels). Consumer Reports found that the Touring Edition with its 16" wheels got 2 fewer miles per gallon than the Standard/Base Prius with its 15" wheels. So that could explain some of the fuel economy difference you're experiencing.

I don't know what could account for the difference in acceleration.

 

Who is we? Are you each driving both cars?

The Touring would be a significant difference. It has a different suspension system.

Also, check your tire pressure on each car. Are they being driven at the same time/temp of day? Are the seats adjusted the same way (could be affecting your driving)?

There are several reasons why the mileage could vary. The MFD is not accurate from about 3-5 mpg, which could explain the disparity.

 

You might check the parking brake on the 2008 to see if it is dragging.

 

I had an 07, and drove an 08 as a rental, and there was a marked difference between the two cars, both were non touring cars, mine was base, the other package 2. Mine had more pep, and got better MPG, the 08 did not get as good MPG even though it was slightly better at getting into EV. I did set the tires to what mine were when I picked the car up, so the only real difference were the tires themselves, maybe, I didn't look at the brand.