Diminishing returns is a cost to benefit ratio. We are hitting the point that the cost of improving the emissions and efficiency by a tiny amount on a car in which both are really good is not just greater than investing in improving those on an average car, but also for less gain. Many cars sold are just clean enough to meet the minimum requirements on a lab test that no longer reflects current on the world drive cycles. The testing means cars that pass are exceeding emission limits on the road. Instead of making the cleanest limits stricter, and having the car companies invest in the R&D to do so, we could see better results in having the rest of the car fleet's emission brought closer to the cleanest cars. A change in the testing procedures to better reflect actual driving conditions will also lead to improvement without even the need of changing the emission limits now.
re. EMF exposure: have you thought about wearing a tin hat, or lining a regular hat with tin-foil? (don't forget the ground-strap!)