My mom used to talk about the cocktail party she threw in her studio apt. in the city. (She had a pied a terre while she was working in the capital and Dad was back in the family home in our town. She used to go home on the weekends to smooch him up.)
Anyway, it was slightly crowded, and there were only a few chairs, and there were plenty of drinks and finger foods. And people on her guest list talked about it excitedly for a long time.
When you're a little crowded, there's a bit more energy. When you're standing, you have to move around, so you speak to more people.
So depending on what kind of party it is, you might find that the chairs completely deaden it. People might sit and be lumps.
I used to throw a big Christmas party; 26 people, usually. I had about 12 places to sit. Some of them were pillows on the floor, or padded ottomans. Those were really intended for perching--people weren't *supposed* to sit down and be comfortable.
People moved around--nobody felt comfortable taking a seat and staying in it, plus they had to get up to get food, which took a while, so they couldn't save their seats, so there was quite a bit of motion through the seats. Everybody got a chance to sit now and then, though they stood for a good bit of the party.
There were a few large TV-tray type things, w/ chairs, that people could sit at to eat the knife-and-fork food, and I found that people would sit there and eat, and then get up so someone else could sit there.
There was a lot of happy conversation, and people seemed really, really happy when they left. And they spoke longingly about those parties later.
I hate parties where everyone sits.
My ILs throw those kinds of parties (and worse, they line the chairs up around the outside of the room; my theory is that it;s because they think having their backs to anyone is rude). They're stultifying.
Get some lively music going, and have fewer chairs than people. Make lots of the food be the kind you can pick up and eat; spread some of it around, but keep most of it centered so people have to go to get it.