I concentrate on one market. I find it more productive to focus on maximizing revenue in one market. I haven't yet found a way to stop coming up with ideas/products for that one particular niche.
I don't believe in diversification when it comes to multiple markets. If you pick the right niche you won't have a problem surviving compared to picking a niche with little growth.
I think working multiple niches will slow growth tremendously while you are able to grow at a much faster pace when concentrating on one. You are maximizing resources instead of spreading them out.
There is no right or wrong answer with this, just open conversation. So, are you faithful to one niche?