OP I don't think you mentioned how you've monetized the websites so far, unless I missed it? That might help people give you a better opinion on how to earn more from it. Again, I might have missed that though so I apologize if I did.
If I were in your shoes, I believe I would just try and scale up the operation which I already have going. If it's only taking you a month to hit #1 for your niche, even if your websites are only netting you $20 a day that's a good sign! Rinse and repeat my friend! If I were you I'd find a template I was happy with (that might be working well on my other sites) and then continue to create and rank them, especially if I had success ranking the others in the past like you do.