This isn't an attempt at advice, rather just wanted to share my thoughts:

If not a niche, an overall thematic consistency is the next best thing. For 'big picture' thinkers, it's excrutiating to narrow things down that much. If it jives with your natural tendencies and brings out your best writing, that is better than forcing a niche. It requires being a real spin doctor and creative outlook. An example is an article I really liked by kyriacos about 'the dark side of leadership' (I dont recall the headline)

Managing expectations of the amount of interest it will gain is essential to keep motivation. Just accept it may get less. That's how I see it.

Also niche is easier for more experienced writers/bloggers.