Amazing list. The only one which i think solves a real world problem is the gay dating website.

I think if you focus on the issues facing every day people and try to solve them you'll find a good niche.

I'm in Norway atm, i found an app that collates all the supermarket pamphlets in a nice layout. It's very useful due to the remoteness of sum parts of Norway.

There's an app in Australia called fuelspy that's widely used to find the cheapest petrol/ notify when best time to buy.

These are all small shops creating and maintaining these apps/websites.

Also have you considered freelancing instead of building these apps?