But I understand the value of working with a distinctly limited number of values - so I'll definitely do sketches with very minimal blending - forcing myself to find the exact right placement for those form-turnings.
Pay attention to the edges of forms!
When you pay attention to these edges you can block in a form with proper values where they belong and end up with something strong and clear. If you instead just go around blending values to the Nth degree you end up with a form that seems to fluctuate and seems unsure of it's solidity. So it's clear that limited value plus rendering form as flat planes with rounded edges can really help to clearly delineate form.