You can definitely achieve more if you can work the supply-side as well. In theory if the smart grid were well executed then it'd be possible for consumers to modulate their heat, charging, tumble dryers etc... to provide more elasticity.
Unfortunately in a lot of places the incentives aren't that high. I don't have that option where I live, but in denver the lowest consumer rate is around 7c and the highest around 17c/kWh. It's hard to invest in new appliances to exploit that difference, but if the off-peak number were 1c then I think you'd see much more take-up of smart car chargers and people delaying when they do laundry.