Re: Fuel consumption - check again!
Have done the same and bought a 159 diesel and like you was appalled at the apparent fuel consumption compared to my 156 now passed to my daughter - but I am not sure the difference is as real as it looks. This w/e the 156 was brought on the same journey (Yorkshire to Bristol) and checked on computer and fill-up. Computer said 55 mpg but fill-up 41.5 mpg. Incidentally the 156 recorded an average, over 2500 that my daughter has driven it, of 46.9 mpg. I just do not believe it, particularly since her 2004 147 only averaged 40 mpg.
Conversely the 159 computer underestimates the economy by 2 mpg on 4 fill-ups I have been able to check. My estimate for real round town ( 3 miles max ) mpg is about 32 mpg, and motorway (70's) is 38 - 40 mpg which would be reasonable considering the 159 is a bit heavier.
One other point, I was loaned a 147 1.9 diesel for that same trip whilst waiting for the 159 and that gave 41 mpg over two ways - motorway only for 450 miles. I had assumed this was because it was new - but I am not so sure now. These are all 1.9 JTDMs of 150 bhp except the 156 which was 140.
So possibly they have slipped up with calibrating the fuel metering - particularly on the 156 which I compared this with and maybe the 159 is more realistic.
Good luck - it is an excellent car and whilst not handling as well as the 156 it is the best ride of all the family estates we tested.