"... If you change your driving style ..." is the key phrase here.
Yes, the extra low-end torque will let you drop your RPMs & hence you should save fuel, but the bulk of the saving would be in changing driving style, not the remap.
If I currently use hypermiling techniques and get 40+% over manufacturer's figure in my 1.6 tonne bus, do you reckon I would see much of an increase in mpg if I had a remap?
Yes - it should give you more power in the low end, so that when you Pulse, you can be in a gear one higher than you would otherwise have used. It also makes it easier to (for example) be in 5th in a 30 zone.
Part of the concept of P&G is to reduce your average RPM - by remapping (and focusing on the low end), you should be able to reduce your average RPM (& hence average engine resistance) further.
However, I would avoid the 90%+ load area at low RPM - the BSFC chart tends to drop off after that point. I try to stick to 80-85% load% when I'm pulsing.
Whether this is cost effective is another question. I have doubts about the cost effectiveness of most mods (although I have had a lot of mods done myself, including remapping... :-) ).
My Fiat 500 Abarth has been remapped, but it was for power and torque, it made little difference to the economy at all.
>...do you reckon I would see much of an increase in mpg...
I should have been more explicit when answering this, yes, you should see an increase in MPG if you adjust the pulse phase to use lower RPMs (closer to the peaks in the BSFC chart), but it'll be small (the reason is that you are only in the pulse phase relatively briefly).
As Draigflag says, I don't think the overall economy change will be particularly significant. I saw an improvement from 72 to 75 mpg when I remapped, but I also modified the aerodynamics simultaneously, so that makes the two mods hard to unpick.
Thanks for the answers chaps - it's probably not worth it for me then, the payback period would be too long. I can do 30 in 6th in my car on the flat without labouring the engine - loads of torque already!