The banners, thumbnails and covers that are used in my teams comic are all about branding, and keeping our image consistent with what we want people to 'instantly read' about our comic. Readers new and old have had a positive reaction to them, plus, they really help you look more professional you know? If you've got a good look in branding, people are more likely to read your comic/be interested rather than if you had...well literally NOTHING there.
We spent a fair amount of time coming up with a logo, and what our branding image would be. While the image is important it's your logos, and characters that people are going to remember. Keep things consistent, change up your imagery if you feel the need (like maybe a big change has happened to the main character and you want to reflect that), but keep your BRANDING the same.
An example of what I mean: Cokeacola has great branding in logo, product shape, tagline and color theme. But their images for ads and their online presence is always changing up. The bottle, logo, message, and color is the same across the board, and even if it's in another language people KNOW Coke. Good branding has that same deal.
As far as reading? If there's no cover, no icon, and no header, I tend to think that the page isn't actually set up? Like they've just started and they're not posting content. So...Idk, maybe it's silly, but images are incredibly important to me. They draw me into whether the mood or idea is something I'd even like.