I've mentioned this before elsewhere but it bears repeating here:
http://www.cbperformance.com/Articles.asp?ID=312
That's pretty far along in a series of articles from Hot VWs Magazine on how to squeeze good mileage out of a Beetle.
The first thing they did was give the whole car a good chassis tune. That picked up about 7mpg right there, jumped from 22 to 29mpg if I recall.
In the referred article they were averaging over 36mpg in busy, high-speed California traffic. 70-year-old design or not, that's pretty good no matter how you slice it. Add in the fact that they enjoyed a big jump in power and torque for a significant improvement in driveability and I don't see a downside.
The stated goal was to achieve 40mpg in traffic, which they never did though they were getting close. And ultimately the articles just sort of stopped, like everybody lost interest. I don't remember there being a final wrap-up, which is too bad. That could have included a final What Works vs. What Sucks chart, which would have been really great for people in the VW community.