I'd pay $4 or so for four new characters and new dialogue. (I say $4 because I figure the characters and dialogue are pretty much 4/5 of the $5 Poker Night.) As far as which characters to choose, I'd go with a few less obvious choices. I can see some hilarious interactions between Bubs, Momma Bosco, Gabe, and the Medic. After all, we already know that Momma Bosco goes to the Inventory based on the opening cinematic.
"Always expect the best of others... And watch as your hope is crushed like crackers in a fat man's bed. And the fat man is angry. And the fat man has a sledgehammer. And the fat man is yelling 'DIE, CRACKERS, DIE!!'"
- Rat, Pearls Before Swine