The best time to have started was 3 years ago. The second best time to start is right now.

I would say to follow your passion. If it would be fun and easy for you to put together some sort of monitoring course I say go for it! I wouldn't worry about people being able to buy it on their own. I know that I could figure out how to snap together these monitoring tools, but if I can pay $8.99 for someone to do all of that research and spoonfeed me the info that is totally worth it.

In terms of expected payout, I wouldn't expect a windfall. I definitely think it would be valuable as a portfolio item, especially if you think you would enjoy a career in teaching/training. If you have a reader base from your blog/tutorials you might be able to leverage that.