If V2G is economically unattractive for car owners to participate, they won't. That's fine but everyone involved knows that. Peak power costs the utilities a substantial factor over base load power generation. There's no reason to think that the market will settle on "a retail kWh plus 20%" rather than on "2-4x a retail kWh".

For $0.04/kWh, I'm not the least bit interested. For $0.40/kWh, I'm probably indifferent. For $1/kWh, I'll buy another car (or fixed battery) just to participate in this scheme.