Steve:
My off-the cuff answers:
1)No the diffrence in fuel economy is not what i would call drastic judging from the EPA numbers and the general consensus among owners.
It <is> noticable though and I know how expensive gas is in Europe.
The FX 35 is a pretty quick vehicle as well, just food for thought..
2) I know nothing about this gas tank, but fuel formulation IN Europe are genarlly the same as most states/provinces in the USA/Canada, except perhaps of better quality in Europe due to the quality of large french italian and german refineries.
3) If you import a car that is not yet sold in your country you are always running risks.I at this point I dont know if the FX is coming to Europe for sure and with which engine fitment (if one one engine choice was offered I supect VH35DE)If it does it will come as a Nissan of course.I think local Nissan dealers would do their best to honor warranties but this is a question best posed to Nissan Switzerland.
On this note the VQ35de should be easily servicable by any european Nissan dealer but this is less certain for the VK45DE.
4) Even if the car never gets officilly imported to Europe ( and I suspect it will) you should still be able to get parts thru the Nissan dealers it might just take longer.
I know there are a couple of early Infinti Q45's running in Europe a car that was never sold there and some Nissan dealers in large towns advertyise "infiniti service".
This general subject has piqued my interest I will research it more and post an update , hopefully within a week.
In summary It kinda depends on ypour budget if you are stretching to afford it I woudlnt recommend the car but if you have a good income and are willing to spedn a bit extra to drive something unique even if it never comes to Europe it will be supportable out of the local infrastructure Plus our club member Joe is the internet parts manager at Scottcsdale Infinti he can send you any Infinti part you want at a good price to boot.
Fred..