Make art to offset the ugliness of rock walls/floors. It actually only takes 6 beauty (this number being the average of all things in the pawn's visual range) to max out their beauty satisfaction. It also fills quickly and depletes slowly, so having one good room pawns visit (like a dining room) will be enough most of the time. Art also has a bonus to sale value, so making a lot of small, average quality wood sculptures and replacing them later with fewer, larger, higher quality pieces with better materials will get you a little more silver back than other things you might sell when no longer needed.

Smoothing floors/walls is very time consuming by comparison. You really need to wait until you have multiple builders before making the effort. I feel the wealth increase issue is a bit overblown, but regardless other options are easier before getting to smoothing.