I made a bed frame out of cedar and will be making matching night stands. I love the smell of cedar and want to preserve it for as long as possible.
Is there a way to finish these pieces, protecting from water marks etc, without reducing the natural cedar smell?
Unfortunately there's little you can do to provide a protective finish (truly protective) that won't block the cedar smell, because the very properties that provide protection do so by sealing the surface to some degree — this is precisely why cedar linings on chests, cedar walls/fitments in some closets are left as bare wood.
As much as it pains me to suggest them, the one thing that might work is a modern "hard-wax oil" but if this appeals to you it might require some experimentation, which won't be cheap given the prices for these products.
My primary recommendation however would be to finish all the surfaces that could do with high-level protection, because they could do with it given how soft American cedars are. And I'd do so in a conventional way (e.g. with wipe-on varnish, a good lacquer) but to leave every other surface bare to maximise the smell. This of course includes the insides of the night stands, but also every non-visible portion of all the bed elements.
Note however that the smell won't linger long on any exterior surface. You can expect it to hang around for a decent length of time only in an enclosed space because there's no constant airflow. This is why the cedar smell lingers for a long time in chests, less long in walk-in closets lined with cedar and not at all on something like a garden planter.
