How niche should your lenses be? As niche as you can get!
For a Rocketmom's assignment last year I wrote a lens on The Best Purple Computer Mouse, now I look at this lens and I can see a lot of room for improvement in the introduction, but it makes sales - why? It's about one thing.
I do have some other computer mouses at the bottom of the lens, but they're all purple so they still all count as purple computer mouses/mice (I still don't have an answer to that question!). When the side bar Amazon modules were introduced I added other purple computer accessories because I didn't feel it would 'dilute' the lens too much.
Now I don't get a lot of traffic, but the traffic I get is very targeted, let's face it if you search for 'computer mouse' you may be after reviews, but if you're searching for 'purple computer mouse' you are usually looking to buy.
This all means that the amount of traffic that converts to sales is a lot more targeted.
Talking niche is often the opposite of talking keyword research. When you do keyword research you're often told to look for something that has at least 5,000 monthly searches with low competition etc. When it comes to niche I will often look at keywords that only have 100 or so monthly visits if the competition is low that is. Why? Because if I can get just 10 visitors a week to a targeted lens that converts 4% of visitors then I consider that to be good use of my time.
I'll talk about assessing competition for keyword phrases in my next post and let you know what I do when researching.