Alex
Nice build. Looks like it has been tearing up a few dusty roads. The only pick I can see is the perrenial decals not being weathered to the same extent as the rest of the tank.
What I have done (and I am not sure that the result was too successful) is a light spray of Tamiya Buff from the wheels up - so it is heavier where you would expect more dust- that gets to the level of the decals. this way they receive a light coat of Buff and this seems to dull them down a bit.
I have tried just using chalk on the decals but it always seems to come off leaving them shiney and new looking.
Brian