It's easy to lose perspective of element size when designing in Illustrator. Minimum line weights are extremely important to keep in mind: stray lines should be at least .35pt for deep relief plates, and .25pt for standard plates. Anything smaller, and lines may get wavy or fall out altogether.
There can be a disconnect between the digital representation and the physical result, so we printed a few line guides. This handy reference, ranging from .35pt-2pts, was printed with a fairly good impression on French Paper, Whip Cream 140c (we also did some on Lettra 110#).
Printing a project with us? We'll drop one of these in with any paper samples we may send your way. No more fingers crossed.