I agree that the auto diesel is unique in the range of Navaras and may indeed deserve its own thread - in any event, we're here now so let's make the most of it!
I have one of these. I'm about 380Kg over nominal weight now, so I should expect around 12.5LPHK. I'm doing better than that (when not towing).
Some of you on this site might know I don't mind throwing spanners at my car in the name of trying stuff out so I can say "Well, I tried this". As an experiment, I grabbed a piece of stainless steel and made me a decent EGR gasket that wasn't missing the great big mass of stuff in the middle (bloody cheap gasket manufacturers). As a result, there's no EGR heading into my engine at the moment.
I've run a few tankfuls like that now, and can say - definitively - that the EGR mod alone seems to have improved fuel economy by around 0.5LPHK.
I have again begun adding 2-stroke to my fuel. I am now using 300ml of Valvoline Racing 2-Stroke in each tankful, as it is also JASO-FC rated. I seem to have further improved the average economy but as I've only run two tanks so far (with EGR blocked and 2-stroke added) I can't say with any precision what the improvement is. Over these two tanks, it looks to be like another .3 or .4LPHK, but it's early days.
I did notice, when trying to move the vehicle slowly last night, that a gentle tap on the accelerator made the vehicle lurch forward from a standing start. It's like suddenly there's more torque from idle. I may be imagining things, but the vehicle feels more responsive with more power. I have no dyno results (and am unlikely to bother getting any) but there's a perception that it's mildly better.
It's not a great improvement, but "a little better" is better than nothing at all.
FYI, the last tank gave me 11.01LPHK. That includes extended driving at 110km/h using cruise control, plus about 100km of city/town driving. Both of these (>95km/h and city driving) cause fuel consumption to rise. I might try and restrain myself and see if I can make further gains, which I know are possible - I am not sure how much I'll gain, but if I can consistently be under 11LPHK I'd be happy.