Up to $1/hour, given the LEAF's rate of charge.
However, I don't think Level 2 charging is of general use for me, since I won't likely be at a single location (except work, airport, maybe the movies) for more than an hour. Rather, DC charging is what I'd find useful, to the tune of $4 per charge.
Now, I realize that there is a high probability that many EV drivers (when conditions are right) would potentially abuse a $1/hour Level 2 spot by leaving their EV in the spot after charging has completed if they deem that price to be a reasonable "parking convenience" fee, leaving other EV drivers without a charging spot. I suppose that's why some folks feel a significantly higher fee is appropriate, as it might help discourage abuse. At present, though, I am of the mindset that there should be two fees involved: a reasonably-priced "charging" fee, and an outrageously-priced no-longer-charging-yet-preventing-others-from-charging fee. For instance, $1/hour while charging, $10/hour while not charging, with a 15-minute grace period once charging completes. The proceeds of the $10/hour fee could potentially be used to fund additional charging infrastructure at the location.