Yes, when it is possible I start with the recessed surfaces and adopt the usual technique: two thick layers of bondo sanding after the second one, and then layers after layers, going thinner and thinner, until the surface is smooth as I want. I didn't use the dremel and always sanded by hands. As you said the dremel is difficult to control in surfaces as the one you've marked, and I work in the stairs of my apartment and I have to keep the noise and dust level the lowest as possible...