there's plenty of cars out there for under £1000 (or waaaay under even) that are decent sized diesels (2.0l ish) some turbo some not, that pretty much all do 50mpg......
In my head, anything above 45mpg is good. (plus it means working out mpg is easy....4.5litres equals 45miles...lol)
Ive had a citroen/peugeot 1.8 non-turbo. did 50mpg no matter how you drive it but was slow at best.
The rover 420 turbo diesel i had 1999, cost me £420 and once chipped (£50) gave around 130bhp and massive torque, whilst still giving 50mpg minimum.
I think if i had to, i could sell the omega for what its worth, and buy another car which did better mpg. That is however not my perogative, as i need a big car and just SOLD the rover instead. I'm making a compromise on fuel for the added space whilst still maintaining comfort (could have just got a van again).
Personally....i think there are plenty of cars out there offering better economy in an equivalent price range to the omegas worth.
just my 2 pence