Thanks for the kind words everyone.
It's not clear on the pics, but I did drill out the barrel of the 37mm gun
I think people were right with their suggestions with regard to:
1) dust behind the bogies
2) silver on the headlights and
3) washing and drybrushing the dust
So I went back to the workbench and these are the results:





I agree it looks better now - thanks for the advice!