I don't think you need to un-publish the non-featured hubs. Just read your hub again from the point of view of someone who knows nothing at all about the subject and then revise the hub by adding more informative content. Maybe add more photos, a video, a comparison chart - anything that you feel would enhance the hub. You also might need to take out superfluous information. The point is, if you write a hub that helps the reader walk away with more information than when they came, your hub will have enhanced their reading experience. That's what I try to do. I don't hit the mark perfectly every time I write a hub, and when I don't write a hub that gives substance, the hub goes idle. When that happens, I go back and see where I can improve the hub. Right now, all of my hubs are featured. But, tomorrow one might go idle. And then I'll go fix it to make it better, if I can.
Some hubs can't be fixed, and it might not be due to my writing talent. It could be that the content is so heavily saturated on the internet that there really isn't anything I can offer that's more or different. In that rare case, I'll know it and I'll just simply delete the hub.