This was the SF Signal podcast question of the week. More specifically, whether covers are becoming more minimalistic.
I think when it comes to classic SF authors and stories the minimalistic covers are a way of showing that they have this status (like how Dickens and Austen have minimalistic covers now, in addition to the paintings, etc.) and making the books more palatable to non genre audiences who might otherwise avoid them. Like how the Harry Potter books got 'adult covers' in addition to the playful kids editions.
Look at the covers above. SF readers might pick the one that has SF elements, but people who 'don't read genre books' will read the versions with more simplistic covers. The covers don't tell you anything about the book, which, depending on your point of view, can be a good or a bad thing.
Literary fiction with SF themes tend to get minimalistic covers. The Road is white text on black, The Passage is a couple of trees. The Year of the Flood gets a poppy. It's a way of appealing to a wider audience by toning down the SF elements on the cover. The Gone Away World was a horrible fluorescent green on fuzzy fluorescent pink (which I think failed, and given the trade paperback got white text on an orange background, so did the publisher).
With regards to covers themselves, back when I had a dearth of books to read, I used to walk up and down the aisles at the store looking for something that intrigued me. Sometimes I'd find new books by reading the backs when shelving (a great way of learning what's available, and you'd be amazed at how many books you can remember and hand sell later by doing this... and how many books you'll end up reading that otherwise you'd never have heard of). Other times I'd just pick something based on the cover. I found some great books that way. Like:
Dhampir by Barb and J. C. Hendee
Night Watch by Sergei Lukyanenko
Song of the Beast by Carol Berg
There have been some books where I hated the covers and loved the books. Like:
Elantris by Brandon Sanderson (I thought it was SF when it came in, because of the cityscape on the cover)
Everything written by Terry Pratchett with Josh Kirby's covers (I can't stand his artwork)
And others with good covers where I just couldn't get into the story for some reason.
Everyone's taste is different, so the covers one person likes, another will despise.
There's also a lot of copying going on. When one cover takes off, others will start to look similar. And there's almost cliches for covers. Urban fantasy typically has a woman with a tattoo on the cover, back to the reader. Or there's a man, often in a trench coat. Switch up the cover treatment and you can confuse readers. Living With Ghosts by Kari Sperring is traditional fantasy but the cover looks very urban fantasy.
So while covers are important (I've had customers turn down great books because they didn't like the covers), what's really important is what's inside the cover. I think most people nowadays will look at the cover, read the back and then read a page or two inside. Still, if you've got a good cover, getting attention from browsers is that much easier.
So, what books have you read because you liked the covers?