There are way more F1 rule changes for the 2013 season than just the engine specifications. The chassis will have a major overhaul as well. The most noticeable difference will be the smaller wings which are will reduce drag and improve efficiency. The rules will allow for a venturi under the car to compensate for the loss of down force. A side effect of these changes is that passing should be easier as the cars can follow much more closely without losing down force. This is going to be very interesting.
I'm very impressed with the way the FIA is handling all these rule changes. It's brilliant to have two top designers to develop a theoretical car that meets the FIA requirements, and then turn that design into the rules. There's definitely been a change in how F1 management works with the teams, which bodes well for the future of the sport.