I currently have a WK1 and have driven a WK2 a couple times now and here's my limited review and comparison....
The WK2 is more refined, feels more solid, and creature comforts are vastly improved. The addition of cooled seats and heated steering wheel is nice. The RHR radio while basically the same as the WK1, has additional features such as bluetooth streaming, USB 2.0 ports, larger HDD, etc...
Acceleration feels stronger than a WK1, most likely due to more torque being available at lower RPM's
Overall, the new SRT is a huge improvement over the last gen. It is built better, fit and finish is better, etc..
The biggest sticking point for a lot of us (myself included) is the price. I wouldn't pay sticker and some dealers are unfortunately adding money instead of removing money from the sticker.
All being said, I wouldn't think twice about getting a WK1, they are solid, reliable, and a much broader support base and larger aftermarket options.