I am totally and completely against to-do lists, but I'm not anti list by any means. I think lists are almost as useful as mind maps when it comes to getting your thoughts out of your head because it gives you a chance to let your thoughts flow. Shopping lists at the grocery store are essential, while checklists for everything from surgery to changing your oil are indispensable. Then there is my personal favorite, the project list.
Often times when people get backed up on their email it's because the issues they need to deal with are projects rather than tasks. The first time I saw "write book" on someones to do list I had to laugh. Now I've seen it seven times, it's no longer funny. We have completely unrealistic expectations of the thought load that our minds can handle and as such most people either set themselves up to fail or they don't reach for the achievements they are capable of .
There are certain projects where I would tell you to break it down into logical steps. You can do this with many different kinds of projects from researching and writing an article, to creating a new online course. You can guess at what the parts are and also try to estimate the time needed to complete each one. If you do that, then you can realistically schedule the time to do each part of the project, allowing you to focus on one thing at a time and not worry about all of the other moving parts. For projects with a clear deadline, this is the path you must take, though it can be applied to open ended projects just as well. However, there are some projects that are more abstract, and that's where things get interesting.
I have a notebook in Evernote called Projects. This is my repository for all of the big things I want to get done like writing books, creating courses, developing new coaching programs, and even new skills I want to learn. Each time there is a new idea for a project I create a note and then I might add a couple details to it, but then - and this is the most important part - I go back to whatever I was doing and completely forget about what I just wrote down. I got my ideas out and now I can move on. You have to realize that this project folder is part of the Optional, it doesn't have a deadline which means you don't HAVE to do it. You may want to do it but that's not enough justification for you to stop focusing on the essential. You should only look at the project folder/notebook if you have a new idea or if you have some free time with nothing else going on. That's when you can allow yourself to get lost in the land of "someday" projects. You may add a couple more lines to a project or even a picture that you find inspiring. The hope is that someday the project will have enough meat to it to make it worth doing and that you'll have the time to act on it. Of course sometimes you add notes to a project for weeks and then as a result realize the project is no longer worth doing. That's just as beneficial because otherwise you would have had a bad idea kicking around your head wasting your brains resources.
So in short, you need to have some repository for the projects that don't have a clear path of execution and are also not required. Doing so will get some really big and daunting ideas out of your head and actually make it possible to achieve those things someday.