I logged into one of my other accounts today to see that daily traffic was up by at least 1,000 hits. I Googled and I saw that my hub is now featured in the top spot (spot #0) in Google, in the answer box/rich snippet.
Just thought I'd share - this is another great benefit of the niche subdomains.
Congratulations! It's amazing that such a seemingly simple thing has had such success. It just goes to show, something that seems like common sense can be helpful, and something people are searching for. Great job!