I too am a fan of a clear finish over real walnut stock, allowing all the grain and coloration to show through. Of the 10 or so stocks I've refinished I've never applied stain to any piece of walnut. If you do choose to go with a clear finish I'd highly suggest a verathane or poly finish (satin). This finish is much tougher than any other type and with no stain underneath, future applications (if ever necessary) are as easy as a light sand and re-coat away.
I have stocks finished in this manner 20 yrs ago that still look excellent (without additional coats). To check for the color you'd get without any stain, final sand the stock to necessary smoothness and wipe with a wet cloth (or one soaked with paint thinner or turpentine) and this will show you what color you'll see with a clear finish.
You can use wipe on, spray on, or even brush on poly and not have to worry at all about over sanding between coats (you won't damage the color or finish by slighty too much sanding). By using a satin finish, rather than gloss or high gloss, you'll have a low luster finish. Gouges or bad scrapes in the finish can be repaired by wiping on some additional finish, or even using a cu-tip or small artists brush for touch up.
Two or three coats of finish, sanded in between, will give you a very durable and weatherproof finish. Remember to finish all areas of inletting as well for a really weatherproof finish.