Is it work making a small bedroom smaller by installing built in booksheves?
Most house buyers won't be going in with a tape measure. If it's likely to be  a problem, your realtor will let you know when its time to sell. They will probably recommend a short list of work to be done anyways (paint is a huge bonus).

In my limited experience as a home-buyer, it wouldn't make a lick of difference. If it looks nice, its a bonus. If it doesn't, I'll plan to tear it off the wall and paint.