Its a aircooled thing - isn't it ?

There are lots of choices in life that we make without being able to justify them. Most of the best ones I'd say. Buying a van in the first place has to come under this heading. No use trying to be sensible about it now.
Shut your eyes, say la-la-la and get the saburu conversion if you want it and can afford it. I wouldn't worry about the petrol saving and the cross-over point when it supposedly pays for itself. Think like this and it won't happen.
You only live once after all.