You can smooth out a cast iron cook surface. It only tales a few seconds with a flapper wheel on an angle grinder.
Wish I'd thought of that; I spent a couple hours at it using an orbital sander, up to 320 grit. No regrets though, that pan is easily my favorite piece of cook ware.
When it comes to seasoning carbon steel you should not be letting carbon build up. It's a bad habit. If your getting carbon build up clean it off with something coarse like salt or a metal scrubber. After that if you need to it's not hard to give a pan a quick touch up seasoning with oil. Carbon steel is much quick to touch up season than something like cast iron. Cast irons rough sand cast surface means you generally need a much much thicker seasoning layer.
You also should still clean the pan too! Modern dish washing detergents are generally not made from lye so won't strip your seasoning.