My wife calls them dust collectors. In the few houses I have seen them in they are usually displaying antique items, trophies and/or misc items.

I would not display anything there. Any décor or art belongs at eye level anyway.

Elf on the Shelf could probably get up to some hijinks there at Christmas but other than that, ignore it is my advice!

Putting things up there ends up being a dirty mess and the problem being it's a pain to get up there so we, "put if off until tomorrow". It's a good idea in theory, yet having had something similar years back I'm stumped. I'm sure somebody will come along and offer a great idea which I don't have.

i'd frame and sheetrock it over. is there access to it from the second floor through the wall? to be added space?

I agree with Cindy, but I tend to make projects too complicated and would try for something decorative, like a colored glass panel, stained glass, etc. that might be on by-pass tracks like sliding closet doors. Perhaps backlight it if you won't use it for storage. The sliding panels would keep dust out so it would be ideal for blankets, luggage, etc.

they're called vaulted ledges. I like the idea of storage and closing it off w/some doors or something? obviously would have to be custom. All I could find was something like this above the bed.

you could do some cool lighting and put it on remote. they have those LED strips that have 25 different colors.

paint the back a deeper color and back light it. or the stencil and one or two items.

but yes, if you don't need the storage and have the extra funds, close it off.

Do you need the storage space? If so, I like the idea for sliding doors painted to match the room walls. Otherwise, drywall it out to match the walls. If you are really short of storage, you could always do one of those library ladders on the rail for easy access

Have some custom cabinets made. Lots of wood choices and melamine choices available.