This actually a great question.
But for a more vague and useless answer, I can give you that ( maybe I'll write a post later this week about it..)
The idea muscle is really a muscle. The more you use it, the better it is and the more it grows. What it means is that it gets easier to develop and "have" ideas as you work for it. Work being the main word here, you need to actually do it. As you said: lists are good but also just pushing yourself to have SOME ideas. Most are bad, that's ok! The more you have, the btter the chance that one or two will be good. Then, who knows..you might hit a winner :)
Another things that helps is inspiration. Now this doesn't mean just waiting for the muse to hit you in the head but actually being "out there": reading, interacting, commenting.
A lot of times, I think I have nothing to say on a subject but after starting to write on it, I find myself with a post or two. Sometimes you do not know until you put it on paper :)
Good luck, fellas!
You are so right, it is just a muscle like everything almost in my opinion. The more we do the better we become or easier it is.
Inspiration is another thing we need to have or create within ourselves. All can be done.
Thanks so much for this great comment @razvanelilmarin!!