My general experience has been that "I don't know, but I'll find out", said to someone currently equal or lower status than me, clearly but mildly correlates with most of the low status behavior you mentioned. I'm not as sure how it affects people higher status than me, since I don't have as many of those relationships / data points.

So I continue my assertion that, yes, it's high status, not merely socially rewarding. I still suspect this is a weird and unusual set of experiences, and probably has to do with how I position "I don't know" relative to others.