I think it will look fine if you paint the risers and the spindles. But don't just paint one...you need for the color to be repeated somewhere in the staircase to tie it together.

kitchenkelly, When we finally got to installing the runner (months and months after having moved in), I was trying so hard to be fine with it--even though I was sure we had asked for it to be wider. Our staircase isn't narrow, so there's enough runner there even with the sizeable amount of wood showing. The runner is 32" wide and the reveal is about 7", not including the wood to the outside of the bannister railings. The installer said something about 6" or 7" being the standard reveal but I think he was just covering himself at that point. Also, our stairway makes a turn, the bottom stairs are wider than the upper stairs, and there are posts that cut in so it was kind of like a geometry puzzle to figure out how close we could get to the posts, etc., and still have it look okay. After the runner had been cut the installer said that we could possibly have had the runner hug the posts but I've never seen it done that way. Not sure how that would have looked and it was too late for us anyway. We're still having a problem with our hard drive but I'll try to take and post photos later if that would help.

They probably put plywood in middle to save $, knowing they’d carpet stairs. My FIL did this in hallway and I hate it b/c if you don’t want carpet, then you have to redo or restain that section. He’s enjoyed it for 50+ years so who cares about next buyer, ha. It is a money saving strategy that allows you to spend more on a runner and those bars some people use to secure runners. Have you ever priced those? Not cheap!

seabornman yes, I agree. that is one of my husband's concerns about this project. If he DIY, he wants a kit that has been designed to be structurally sound. This company here (https://cheapstairparts.com/pages/how-to-install-a-wood-newel-post) has some good installation instructions. I am getting a few more quotes this week, but if not I think we DIy using this company's kits.