Love the cabinets. Yes I would put similarly sized pieces over the cabinets. Look at sites like minted.com for reasonably priced art

Is the TV a bit high?

TV above the left cabinet, art above the mantel, shelves above the right one.

Art, yes.  Try local art shows and exhibits. I've got a lot of art on the wall, either orinpginsl or numbered prints, and most pieces have been a few hundred, not thousands, of dollars.

Meg - I only decorate with pieces that mean something to me. I often use photos I’ve taken from some place special and have them enlarged and framed for the space. One of my favorite all time cheap pix is of the “Imagine” mosaic piece made for John Lennon at Strawberry Fields in Central Park. I get so many compliments for a $12 photo and $20 frame with a museum mat.

Do you sit right in front of the fireplace? If not, I'd move the tv to one of the sides. That'd let the fireplace be the centerpiece of the room.

Also disregard the TV size chart above. It is for if you want a theatre type experience.