Lately I've been thinking about this and I feel that it's a prime example of a situation where it's better to measure than assume. I get the impression that there's a particularly compelling assumption to be made that getting people into closer proximity will lead to more social interactions, this tends to be unquestioned however. It has always seemed to me that more interactions doesn't imply a higher quality of interactions, but the underlying assumption that it leads to more interactions might not even be true.
The other day I was in the city and I noticed that there's large crowds of people and that people not interacting as much unless they already know the other people. And this is in absolute terms not just percentage terms for some people. In regional areas there's fewer people but the times you bump into people you tend to have much higher quality interactions, even if the people you bump into are strangers you tend to say hello at the least. I wonder if open plan offices have some of this sort of effect going on.