So my elevator theory was completely wrong. People who take the elevator are anti-social grumpy people with frowns who don't want to engage or even make eye contact. But mostly, I end up riding the elevator solo and just wasting electricity and not getting any health benefits.
Turns out the stairs was the right approach after all. Lots of eye contact, lots of smiles, and actually more time to interact as one is going up and the other going down. And I've had a few times recently where I've ended up doing a couple of West Wing walk-and-talks down or up the stairs with people.
So back to the stairs for me.