Hi Michal,
I can´t see why you consider to do the paintjob again. The cam scheme is excellent airbrush work. Also the dust. So, what makes it look unnatural to you? From my point the vehicle is too clean on the upper surfaces, especially the turret top. Imagine, if a tank goes cross country, the dust sprays all over it, if there is mud and water, the water sprays all over the vehicle when driving fast. Even if the vehicle was complete dirty at a time and then was carefully washed, the colours never again looks that fresh again as when painted in works. It is not a gloss finish like on cars which looks clean after washing. A tank´s colour from my point is a little rough in surface and therefore it won´t be clean at any time. A tanker washes his vehicle from mud, that´s all. So, the colours do look too fresh on the top surfaces on my opinion. Also, the crew enters the vehicle with muddy shoes and walks around on the surfaces. That brings dirt on these surfaces too. After some days on exercise, there are lots of muddy footprints on the vehicle. You have to maintain the vehicle, the engine deck, etc. when on exercise. 4 crew members do lots of foot prints!
So, keep it as it is and work a little more on that beautiful base colour. But-just my opinion. Go for some pictures of really dusty Leos, no models, but the real thing. I am sure you will find lots within www. And remember, dust/mud water not only sprays over a tank, it splashes if you go cross country fast! Heavier on the bow and front, smaller sprinkles if it goes further back (turret etc.)
Andreas