Listen, forget about niche specific when it comes to followers. Follow anyone you find, especially of they have a lot of people following them. Your pins are going to show to all of your followers, but if your follower pins it it will be shown to all their followers. These "followers followers" are not likely to be in your niche anyway.
What matters is getting eyes on the pin. The more people who see it, the better chance it gets clicked on or shared.
Follow everyone who comments, likes, or repins your stuff (comment on the ones with alot of followers first helps), many times they will follow back. I only have 2900 or so followers (all of whom followed me of their own accord, usually after I followed them) but some of them have over 15 thousand followers, and a few even more. I don't care if their followers are in my niche or not, any time they repin I get massive exposure. The repin brings more people into my boards to see the other stuff.
Remember Pinterest when you travel the Internet, and pin neat crap you find.
If you make your Pinterest account about one thing, in my opinion it seems commercial. It obvious its a business. If you have boards about all kinds of interesting stuff you look like a person, and you can throw all kinds of interesting money hooks out there.
For the record, I have never tried a single focus Pinterest account, just my personal one, so take that in consideration.
