It's nice to be nice, of course. It's not BAD to practice random acts of kindness. But if you want to build your happiness based on the happiness you bring to other people - the noblest ways of boosting happiness - I think it's more productive to be targeted. Hold the door open for a person pushing a stroller. Give your seat at Starbucks to an elderly person. Help a co-worker even when you're rushing to meet a deadline yourself.
Except for the "Help a co-worker" part, these are things I always considered expectations, not "kindness." Helping a woman with a stroller -- what man wouldn't do that? In fact, I always hold the door open for women, stroller or not, and see this behavior in other people as well. I wonder if this is a situation where Rubin, a New Yorker, is used to a different set of behavior norms than the rest of us.
And talk about awakening fears of "reciprocation" -- helping a co-worker is the single best way I can think of doing that. You should only do it if you know them well and are already friendly with them, they are in no position to do you a favor in return down the road, or they know, and accept, the notion that eventually there's going to be a favor called. Anything else and you are risking uncomfortable personal dynamics in the one place nobody needs them. That's just the way the real world works.