To my delighted surprise, I quickly found that the light sanding was ruining the paintjob but in a very positive, realistic way. I had planned for this to be a highly weathered aircraft and the sanding of that pebbled finish was bringing out a very believable sort of fatigued look to the paint scheme.
So I started out light:
Gradually building up the various effects with a combination of paint, pencils, shavings dust from sanding down various colors of dry pastels, some silver Prismacolor pencil touches for chipped paint effects, and Tamiya panel accent fluids in grey, brown and dark brown. My goal is usually to end up with a purposely over-committed weathering effect. Now I realize all the pros will tell you to avoid overdoing weathering, especially on aircraft. Which is quite true when it involves viewing finished models in person at well-lit modeling competitions. But I find with my final diorama images, more is actually better as it registers on camera (for you folks!) better than limiting the weathering to remain subtle. Besides, weathering is so much fun! So I purposely overdo it a bit as you can see in the last photos below: