You never mentioned your site on here. After a little digging I found it: http://www.justinring.net/
So as far as your question goes, a domain that states what you are trying to accomplish would be great! If you do that are you going to keep going with your initial site?
I definitely understand your frustration with buying multiple domains and not hitting it out of the park with any of them. I can attest that it takes several tries to get it right. The path to success is laced with failures, those are what you stand on to elevate your perspective!
Do you have a coach? Having a coach will cut your learning curve exponentially. They can save you from several mistakes that will cost you time and money. Just make sure that the coach you are working with has done something in business that would give them the experience to guide you!
No reason why you can't have more than one web site. That said, what is the brand you want to develop? Something that makes a good book title or your own name? I think you need to figure out the structure of what you want to put together and then it might dictate the best direction to do in.
It sounds like you're struggling with follow-through. My advice is simple. Make a list of the behaviors you believe are needed to achieve your goal. Start executing on those behaviors every week. For example, if you will need to write a blog post each week, do so on your current platform. Get into a rhythm of the work you know you need to do to launch a successful platform. Then, whatever domain you purchase or platform you launch, you'll be set for success.
I have similar issues with follow-through from time to time. Usually, in my case, this happens because I get discouraged and don't surround myself with others who will hold me accountable.
To answer your actual question, a focused domain is great. Just don't spread yourself too thin. For example, if your current blog requires a weekly post and you commit to two more for a new platform, it could overwhelm you. Focus is a good friend.