It's a little odd with the glass shelves in a Kitchen location. Having said that, by painting the interior of this niche a fresh color you can achieve a lot. I would not go dark but use something that brings some contrast. Light Blues, Greens, or a pale Gold tone will work. For the top shelves see if you can add some glass or objects that are translucent. If you like the country flavor, pressed glass plates and cups are a possibility. Cookbooks are of course a good choice but use sparsley and toward the lower portion. If you'd like this a little more contemporary, remove the top shelf and start with something tall. Then work downward with plates, dishes, and books.

something whimsical (child-friendly) on the bottom 2 or 3 then your collection of ?? bright, pretty glass or ceramic.

Are they glass shelves? I think I would put 1'' thick wood shelves in there and then fill it with books. Maybe a wood or wicker box in the lowest part.

Cookbooks.

If you get some nice collector plates and get something to mount them on, then I would put one dish per spot

Here is one example.

http://www.sustainable-furniture.co.uk/images/uploads/3%20shelves%20and%203%20baskets%20tall%20unit.JPG

If you have a cookbook collection, agree with others this is the perfect niche to put them in. Since they will block the light, you could just put a nice piece of pottery/china at the top for it to shine down on. Be sure the shelves are tempered if you are putting books on them; if not replace with would and paint them and interior to match your decor as suggested above. It's a fabulous niche.