Putting side skirts (Schurzen) on a Dragon Brumbar: they're metal and very thin, so they should be scale. I've never used them before, and I'm not sure how to approach painting them. I use a simplified modulation technique (glorified way of describing altering the shade of the color). Normally I'd paint upper surfaces on the top hull lighter than the lower areas (it varies) and vice versa with lower hull. However, not sure if these skirts would benefit from anything like that (mud and dust natch). Would it be a good idea to paint them straight up and then apply filters and oil embellishments and forget shading?

Since they are a flat vertical surface, they would not cast a shadow on themselves. Try making the inside darker on one and on the outside of the other. Even though the outside would face away from the sun, it should not be too dark.

Everything in moderation would be OK in my opinion.
I do believe colour modulation works when done well and not having too much contrast. It all depends on many weathering stages you would normally do. When watching to DVDs of these techniques they have strong contrasts to show clearly what they are doing and also to have some of the effect visible after loads of steps, including filters, washes, rain marks, oil spills, chipping, rain marks, more filters, pastels, etc. If you have less steps or weather less, reduce your modulation accordingly.
This should be the case for your schurzen as well. A slight fade in colour towrds the top ... maybe even front to back as well ... would work, but also remember your weathering will follow this pattern as well. The lower and front edge of the schurzen will get the brunt of the abuse as well.