I agree that many modern book covers are overly simplistic with blocky colours and tend to be fairly boring and unrelated to the book contents. On the other hand, some older book covers are clearly meant to be displayed in colour and appear as an unfortunate hodgepodge of grey on an ereader screen.
I generally don't buy physical books anymore, and for ebooks I enjoy having the book cover displayed as a screensaver on my kobo, so a nice cover is relatively important.
If I get an ebook with a horrific cover I like using the
Penguin Classics Cover Generator to create a new cover and update the ebook in Calibre (where the generated image is solely for my personal use of course).
For example, I didn't like any of the covers available for Labyrinths by Jorge Luis Borges so I made my own with a quickly googled image of a maze. Not particularly inventive, but considering it only took about 1 min total to make then it's not bad.