I am a huge diesel fan, and have owned many from Peugeot, VW, and Mercedes-Benz. But one thing gives me pause here - you have only driven 100K in 15 years! So sure, the diesel will do better than the 328XiT, but with such minimal driving, does it matter? I get 30mpg on the highway with my 328iT, the 335D will do at best 10mpg better, with about the same difference in the city. The diesel is a bit faster, but the 328i is already a pretty rapid car - don't let the turbo contingent on here convince you otherwise. The diesel WILL cost more to maintain, and while I personally am in no way a fan of AWD, that is a possible concern for you as well - you can't get an AWD 335d. I'm a wagon guy, and a manual transmission guy, so for me there was no question of which version to buy. The wagon is just so much more useful.
Now if BMW sees fit to bring the f31 here with the diesel, especially the MUCH more economical four cylinder diesel, I may have to trade cars. But I drive more than 20K a year.
'11 328! Touring - Tasman on Chestnut, 6spd manual, factory upside-down "i" option