Reading the mileage for you guys with the newer Doblo has me a bit worried. Was going to invest in the latest after this one goes, now not so sure.
Anyway, I have the 2002 1.9 JTD. Vehicle was stored (garage) for 5 years while the family decided what to do with it. After tires, hoses and full fluids change, she gets 40 to 45mpg city driving.
Made a couple UK to Italy trips where she'll average 65mpg. Going down hill (if yer careful

) I managed 71mpg.
Driving style is a major factor with mine. Shifting always at 2K, only going above 3K in fifth. Keep engine breaking to the absolute minimum. Also even distribution of cargo, maybe a little more weight slightly forward.
Doing all this easily get 60 without to much work, but still 65mpg is the standard for 1000KM trips.
Before very long trips, where I know I'll go through a full tank, I'll add a injector/fuel conditioner as well as an oil additive for diesels.
Considering her age (but I do like older women) she has been by far the best used vehicle I've ever owned! Engine has 150K kilometers on it and no signs of stopping!