can i ask why the tv is mounted right next to the doorway?

whites and creams will contrast well, so would light blue yellow..

try stacking a few books vertically, and then adding a few things to the shelf.

wouldnt put too much on top of it.

Whatever you do to the bookshelf itself, you should lower the tv to just above the bookshelf so the wires don't show and center the tv over the bookshelf.

I'd not put anything else atop the bookshelf other than the tv. Instead, create a knickknack shelf for such things either above the tv or beside the tv or just repurpose the other items elsewhere.

I've seen this shelving done with the back board the same width as the shelves:

http://stogielife.com/wp-content/uploads/new-furniture-decorating-for-gold-white-wall-shelves.jpg

Can't tell on my screen if the bookshelf is painted black or wood but with a very dark finish. Unless the bookshelf is a really good sturdy wood that you believe could strip and end up with an attractive wood finish, repainting is likely the most practical way to refinish the cabinet itself.