In a recent interview, Vergne said his qualifying woes were at least partly explained by two things: 1. getting the tyres up to temperature/to work (which should be easier on this year’s tyres), and 2. Setting the car up with understeer, because in the races the cars are rear-tyre limited, so an understeering car in qualifying will give you a better race car. I don’t know how that will be in 2013. Bottom line: in 2013 JEV need not be a bad qualifier.
I think the really interesting part about Q1 will be: which top drivers will dare not to run the option tyre, and who will make a mistake on their first flying lap, because, as @me4me pointed out, it looks like you only get a single decent lap out of 2013 Pirellis.
On pure pace, I suspect Toro Rosso will be the slowest midfield cars for the start of the season, as they have focussed on improving mechanical grip first, I think, with aerodynamic improvement coming later in the season. Of course, Melbourne is not massively aero-reliant, so they may escape Q1 there anyway.