I've tried to use some of these mentioned GUIs. For me, the learning curve is fairly steep. Beyond creating something very simple I always find myself spinning my wheels very soon. I know what I need, so it's much easier to jump into the IDE and just do it. Also. At some point even your HTML is going to be made live. Either through turning it into the template or inline code or etc. it just doesn't really blend with my workflow. I prefer to sketch out things on paper then just go straight to IDE seems to be quickest way to keep the iterations going and then push to prod with least amount of friction.
I see using these tools like using photoshop to create a sculpture.
I completely agree with the learning curve. I often think it's just as hard, if not harder, to learn a new tool than it is to learn a new programming concept. You have to re-train your brain to think the way the creators of the tool approach problem solving (assuming their approach is actually good). If you're not already like-minded, then this is incredibly counterproductive.
There's so much flexibility that allows for creativity when you just understand the code. In fact, I've been doing what I consider to be "designing in the browser" for years. Which is using Photoshop to get started, pick colors, etc, then utilizing developer tools for much of the refinement during the implementation phase. This is the closest thing I've ever found to a good "GUI editor".
I see using these tools like using photoshop to create a sculpture.