I think the new engines could be the biggest differential in form next year.
Pirelli are likely to construct a tyre with far less dedgegation for next year because it's got to the point where the resultant beauracy within F1 has created too much negative publicity for them so I expect the 2014 tyres to be behave a little more like the old Bridgestone era in some ways although perhapps not quite in that extreme.
I think we can reley on Adrian Newey and Red Bull to design and build a chassis which sets the standard. But I think the question lies in who out of Renault, Mercedes and Ferrari will have done the best job in developing the new 1.6 litre turbo engines and the newer KERS. Who will be most reliable? Can we realistically expect larger gaps between the performance of the engines than produced by the V8 era?
Next year making the difference may be outside of a driver's capability. It could well be beyond even a Vettel, Alonso or Hamilton to compensate for a substantially underpowered car. If one of the engine manufactures blunders we could even see a major shakeup in the form book. For example if Renault build a turnip of an engine and Mercedes build a peach then Red Bull could be vulnerable to Mercedes and McLaren, maybe even Force India but possibly not Williams
Similarly if Ferrari build a corker then the day glo orange cars could return to championship honours and Maurussia could actually catapult into the midfield (that's slightly unlikely
)