I think the most useful sculpting tool, besides the main one, is erosion. Not smooth, erosion. It seems like it makes more of a realistic erasure of sculpted peaks. The smooth is useful, sure, but erosion is likely the tool to go to for when creating those oh-so realistic triple-A games that haven't heard of an art style. It is also more powerful than smooth. Erosion feels like a bit of a mix between flatten and smooth in how it works. Its got gusto, and I like that (reference?).
My main challenge with making sculpts look realistic is the tendency to make mountain peaks when sculpting. There are tools for that, of course, but it still keeps crawling back to the same formations. Smooth and erosion seem to be able to fix this problems well enough.
Using reference images would mostly give me a more solid idea of what I want my landscape to look like. Actually attaining that goal would still be hard, but it would be better than doing the whole thing blind.
Separate Modeling Experiments