RE: details vs. plot-- they are not, as you keep pointing out, Theresa, mutually exclusive. Details can help support and drive the plot, and to paraphrase van der Rohe, the theme is definitely in the details. It's a matter of choosing details which reveal more about the character, the situation, the conflict. That's what is going to distinguish a sophisticated writer-- ill-chosen details, or none at all, are a Mark of the Amateur (I think we ought to apply for a trademark for that).
I also think that the advanced READER wants more than just a plot. Someone who has read two novels a week for twenty years needs more texture, more interactivity, more continuity, more coherence, than a new reader would need.
Any novel that can be reduced to a few Twitter tweets, well, that's a novel that might appeal more to the new reader than to the Constant Reader.
It's a little complex when it come to marketing, as there's no doubt that many best-sellers are "just the plot, ma'am". Why is that? It's because to make book a best-seller, you need (first option) a very large base of readers, and that usually happens because you've been publishing for many years and have gathered fans with every book (Stephen King, say, who uses plenty of details :). Or (second option) you need to grab the one-book-a-year buyers in great number, the ones who buy the latest novel as a gift for an acquaintance, or need a book to read on the plane and don't have, let's say, the towering TBR (to be read) pile that you and I have. Those readers buy the books that are marketed heavily (and easy to find-- you don't need to go to a bookstore), and because they're newer readers, they don't "parse" the details particularly well, or even notice them, and don't need them. A book with a strong or sharp plot and a fast pace will appeal more to the new reader. Nothing wrong with that... but to reach those readers, to get the level of publisher support required to market to those readers, you have to get an editor to buy your book first, or really, really inspire marketing to write great jacket copy. :)
So I don't know what the route to best-sellerdom might be for any individual author. I just know that most of the books we all love-- and we're Constant Readers, aren't we-- are not "just plot". They're NOVELS. They start with plot, maybe, but they don't end with it. They provide a story that will (we hope) satisfy the newer reader, but characterization and detail and texture and subtext that will add more interest for the sophisticated reader. That's the reader who will buy your next book, not to mention blog about it and recommend it to his/her friends and send you fan emails and suggest that the local library buy it. You don't fascinate and enthrall readers with "just plot". And I don't think you maintain a reader base, book after book, without appealing to the Constant Reader.
However, I'm not naive enough not to have noticed that many publishers have decided that the New Reader is the only one who counts, hence the constant chase for the next trend, the frenetic search for the next (for two years) best-selling writer, the new emphasis on looks and performance in authors (so they can look good on the Today show). I also notice that the industry as a whole is losing the Constant Reader (go figure), and doesn't seem to care much. But there should always be Good Books (any type of book can be Good-- I'm not being elitist here), and there'll always be readers (I hope) who will seek them out. And I hope there'll always be writers who challenge themselves to attain the next level, even if commercial success and best-sellerdom eludes. There will always be a need for story, and "story" is far more than "plot," as Sophocles, Shakespeare, Dickens, and JK Rowling taught us.