There will be a C250 (1.8 turbo) gasser in the US in 2012 that will easily eclipse your 300D. As previously mentioned there are plenty of cars that meet your criteria and exceed the 300D in fuel economy. But I agree that FE hasn't progressed as much as it should have in the last 30 years. Not in this country anyway. $4 seems to be helping.
http://www.autoblog.com/2010/12/22/officially-official-2012-mercedes-benz-c-class-gets-new-four-cy/