The 2014 Revolution has a protected transducer pocket which makes it really easy to securely mount a fish finder transducer on the kayak, and it has through-the-hull fittings which make it really easy to run wires between your fish finder and a battery inside the kayak. 2014 Revolutions come with a bracket for mounting Lowrance transducers, but if you want to install a different brand of transducer, you can buy a bracket for that brand for a couple of bucks.
There are other ways to mount transducers on the 2012 model, including drainage hole scupper mounts (which won't protect the transducer as well as the covered pocket on the 2014 model), through-the-hull mounts (which generally deteriorate the performance of fish finders), and over-the-gunwale transducer arms (which may get in your way when paddling and landing fish, and usually need to be swung up every time you come into shore). There are additional costs and/or hassles with all of these methods of mounting transducers. Like you, I could have saved a couple hundred bucks by buying a 2013 Revolution rather than a 2014 Revolution, but after considering the options for mounting transducers, I bought a 2014, and I'm really glad I did.
However, the 2012 Revolution will do fine (a) if you never intend to mount a fish finder on your Revolution, (b) if you have or intend to buy a fish finder with side imaging, which won't work well if the transducer is in the 2014 transducer pocket, or (c) if you want to assemble a complete fish finder/battery/transducer arm unit which mounts on the gunwale of your kayak and can quickly be moved from one kayak to the other.