Throw out the rules. Chairs don't have to match, and art does not have to be so serious. This room is airy and elegant, and not the least bit oppressive.
Instead of a matchy-matchy dining room set, mix a bunch of styles.
One way to mix up chairs is to buy one style in an array of colors.
Add extra energy with unexpected art and light fixtures.
Replace a few chairs with a bench.
Use a round table to promote better communication.
Don't be afraid to go totally eclectic!
Informal floral arrangements can turn the formality down a notch.
Add a blast of red to lighten the mood.
I keep picturing Jennifer Beals finishing up a dinner here, shoving the table aside, and stomping up and down to "Maniac." Clearly, I am seriously stuck on Flashdance.
Use warm textures and colors.