content tiredness

Yes, I think you can occasionally get that when writing daily, which is not ideal. And waiting to have something worth writing about can work, and would improve the quality of the posts, given that you probably take the time when you write less often, but, at the same time, I remember when I took a break from writing it was very hard to come back, find my ideas and get back "into the flow". So, you identified correctly the risk of making a habit of not writing content.

Regarding your questions, the first and third can sometimes go head to head, as someone's life may not be entertaining to read about, but that person still feels the need to write about it occasionally. Same with opinions, I guess. Some may not be enjoyable to read, they may be rants or capture partial truths, especially when not properly documented (as they often are). Useful, I agree. As a daily writer, I strive that at least part of my posts should be useful to my readers, so they can get value from them. They can't all be like that, but it's important to have something of value people will return to your blog for.