Remove everything from them. Then place one or two small plants on them just so they can be read as shelves that can hold something. No trailing plants. Less is always more. A small pop of green is never a bad thing.

I too would remove everything but a few books. Shelves are for books, not decore TECHNICALLY. Nothing at all on the top top of the case. Display should reflect that. Just curious what is that piping on the wall behind the computer?

Another option is to remove the shelves, repair the walls, repaint.

Yes, clear out most of the items, but keep in mind that the shelves in one bedroom aren't going to have much of an effect on the sale of the house. That depends on your market, the condition of the rest of your house, the location, etc. All else being equal (which is almost never is) the house should look clean and well cared for, with minimal decor items.