I think heel-toe downshifting is a good skill to practice for street driving, not just high performance driving. I will give you one scenario that I encounter occasionally to demonstrate how heel-toe downshifting can increase your safety while driving in traffic.
Think of times of moderate to heavy traffic on freeways or city streets, in which there are a lot of cars and your speed is varying so that you are doing a lot of 2-3 and 3-2 shifting to keep with the flow of traffic. In a car like the NSX you usually can't see over/through/around the car in front of you so you have to be more alert and react quicker to sudden stops from the car in front. When you are doing a 3-2 downshift as the flow of traffic slows, it is good to heel-toe in this instance so that your foot never leaves the brake pedal, in case the car in front of you suddenly decides to panic brake. This happens to me often enough to have made a mental note of it. Just food for thought.