Thanks for all the replies. I have been mulling it over and have yet to come to a decision. My gut feeling is that filling the tank up once a week may be a step too far.
I have to fill up my Derv once a week! and I get 6-650 miles per tank..the Busso would have been two fill ups for sure for me....fuel was the only thing stopping me, and here is why..
other than oil every 5k at least if you are sensible, i'm not sure the Busso has many issues that are not also a potential problem with all GT's (wishbones,electrics,door handles,slave cylinder,water pump and cambelt) to name but a few. the JTS engines are just as sensitive to oil starvation as the Busso, as are the 1.8 twinnies in some GT's.
you could buy a bad 1.9 and have to do all of the afforementioned in the first 6 months of ownership! and on top of this if your turbo goes pop you are in for a huge bill for a new one, even a re-con will cost around £250 ,there are also swirl flaps, egr cleaning or the cost of blanking, the obligatory re-map so the car is fun to drive and then the inevitable new clutch that goes with it, and if you are very unlucky new DMF. in short there is a lot to be said for a naturally aspirated and actually very simple 6 pot.
your initial question was heart or head, well TBH you don't buy a Busso with your head! for that matter you don't buy an alfa with your head. Almost any other Marque offers better economy reliability and even performance out of the box..
none look like an Alfa though and that goes doubly for a Bertone designed GT in my book, when sorted they offer much more than most cars, style substance practicality and drivability in a beautiful Italian package...and nobody would argue that the V6 is the engine that best suits it, all of us that own Dervs or JTS engined ones made a compromise based on our daily requirements, and we know it.
so in conclusion
if you buy a good one other than fuel and road tax IF you do the regular oil services and filters (air,cabin,fuel and oil) yourself and can stretch to coolant changes brake pads and discs when required then it should only be marginally more expensive than the diesel to run, however if it does go wrong it WILL be expensive.
one final thought, if any of the other engines go terribly wrong a replacement engine can be fitted for under £1000, with the Busso its fix it or scrap it...a replacement if you could find one would cost a small fortune.
so this all comes down to finding one that has been properly maintained, because they are relatively cheap to buy they fall into the hands of people that can't afford to or don't understand how to maintain them, I could buy a Maserati GT tomorrow, on my current mileage though couldn't afford to properly maintain it. the GT falls into this category but a V6 can be had for as little as £3k!
meaning they are often owned by plonkers with little or no mechanical sensitivity or respect for the car or marque.
buy one, but make sure its absolutely spot on.