Here's an easy and dramatic refresh: add backing to a bookcase.
My IKEA bookcase was being used as a media unit, but when I changed it out to make it a proper bookshelf in my living room, I added a wallpaper backing to make it pretty and help the items on it stand out.
It was simple and cheap- I cut thin foam core board from the dollar store to the size of the bookcase, and wrapped in wallpaper I had leftover from another project. Then I used black duct tape to tape it to the back of the case along the edges, so that it blended into the black of the case.
I'm all for finding simple and sustainable ways to refresh your space without buying all kinds of new "stuff".