"Regenerative braking takes a lot of complexity to make it effective, and then it is only marginally worth the effort. "
Regenerative braking could be as simple as a friction drive rubbing a wheel only when needing to reduce speed and not rubbing any other time. Nothing complex about that, kinda like those little bike generators to power a head light and brake light, you know those ones that don't work when you stop riding. Friction drive an altenator like that and nothing complex at all, just a lever to pull it into place like some of those parking brakes between the seats, or a third peddle on the floor where a clutch would normally be if you don't have one. 4rth peddle if you do have a clutch 
Very simple and easy, only adds the extra weight of an alternator, battery cable, and lever and cable to enage it. Before anyone pops up with saftey concerns on that idea, some semi's used tire chains that work the same way. Friction drive rubbing an inside drive tire rotates a hub with tire chain sections attached and that slings them under the drive tires as they drive icy roads. You can see them hanging under semitrators if they have them installed, looks like maybe 6 chains hanging down together near a wheel. Maybe 12-24" long? Those are air activated from the cab with a switch, air pressure pushes them down against the tires when needed and a heavy spring holds them up when not needed. Same thing could be done safely with an alternator and cables. Maybe one each side and use two alternators for even load on the tires. Or make a flywheel type plate to bolt to the rearend and drive shaft and friction run it there for even load to both back wheels. Many ways to do it easily. And for any downhill drives it would work well, like for me most driving is up and down! if I drove a level path town would probably be 9 miles away instead of 12 miles with all the ups and downs along the way.
"keep distance between you and the driver ahead "
I agree with that from a saftey point of view, but that is not correct for feul savings of any kind. Following the vehicle in front at a correct "but to close" distance actaully saves you the feul or power, in racing it is known as drafting, it increases drag on the vehicle in front causing them to use more feul and they are kinda sucking you along for the ride behind them saving you fuel. I consider it to be a stupid thing to do on open highways, but much of the time that is what that tailgater behind you is doing! Other times they are just to stupid to leave a safe distance. That is why we are required to have those stupid third brake lights on all new cars, people are to stupid to follow at a safe distance far enough back so they can see the old normal brake lights so we have to have them mounted higher in the back window that bothers us while we drive at night so those tailgaters can see when we put on the brakes, the other ones are hidin by their hood because they are too close in the first place!
Otherwise I agree, alot of feul savings rather electric diesel or gas depends on driving style and all the other known things like keeping tires inflated properly etc.., but if you already do all that then there is nothing more to gain, so Regenerative braking, solar pannels on the roof, and a windmill to raise when parked are about the only extra options to increase milage
