A machine like this should be cheaper (smaller, lighter, fuel efficient, less crew) and have more applications. It's not to be another Nimrod. E.g. MPA could transfer excess fuel if they relieve eachother in patrol areas.
I think you're overlooking development costs somewhat. There's little point in a fuel efficient aircraft if it costs twice as much to purchase. You're using a new design radical configuration which will be expensive to develop and all the small efficiency improvements in the world aren't going to make it financially viable compared to something like the P3, which we could buy off the shelf tomorrow. Heck I bet the Americans would even throw in some discount training stateside and some spares rather than having to start with a new type from scratch.
I'd also challenge the idea of smaller and lighter. If there's one thing that's been learned during the development of Sentinel it was that small aircraft run out of space more quickly.
The fueling issue, potential to receive fuel would be useful (but not essential if it's got a 12hr plus endurance anyway). Delivering fuel is a waste of time, this is what we've got tankers for. If we wanted to have a flexible multirole tanking capability we'd buy the add ons for A400M which would make it into service far sooner than a new build aircraft.