Great question! This is a classic challenge when working with meshes in AutoCAD. When you increase the smoothness level globally, it acts like a blanket smoothing filter and ruins hard edges.
To keep sharp features intact, here are a few approaches depending on the model:
Creasing Edges (MESHSMOOTHCREASE): Before increasing smoothness, you can apply creases to specific edges or vertices. This tells AutoCAD to hold those edges sharp even at higher subdivision levels.
Selective Refinement: Instead of cranking up the global smoothness for the whole object, try refining only specific faces or sub-objects where smooth transitions are actually needed, leaving critical mechanical features alone.
Hybrid Modeling: If precise dimensions and sharp intersections are critical (like for manufacturing components), I usually avoid heavy mesh editing and stick to solid modeling, or convert the final clean shape back to solids using CONVTOSOLID once the organic parts are done.
How complex is the geometry you're working on? Are you dealing with mechanical parts or more of an architectural/organic shape?