There is an old question that you'll hear sometimes, "Do you want it fast, or, do you want it accurate?" The pith in that saw is that there is a trade off between doing something quickly and doing it correctly. But you can really take such maxims only so far, because the truth of the matter is that speed is a part of accuracy. If it isn't on time, its not accurate.
In the same way, production values are part of content. If you don't have high production values, then you don't have good content - you just have good ideas. And as Monte has said, ideas are aren't even worth a dime a dozen. They are more like a nickle.
Now, to back away from that a little bit, its easier to have crunch without what first comes to mind when thinking of 'high production values' than it is to have fluff without same. Crunch probably works best in rows of neatly typed, neatly spaced text under regular headings. At least, that's the sort of crunch I find most inspiring. But the 'high production values' of crunch is hidden from the eye and only shows itself latter on. The high cost of producing good crunch is playtesting, refactoring, and then retesting. So much of what has been produced for D20 over the years suffered (and suffers) from hidden low production values.
But you specifically said setting, so I think you were thinking of art: custom calligraphy or fonts, illustrations, narrative fiction (another sort of illustration), poetics (take Planescape's conciet of 'cant'), etc. You are right. You arent' going to even attract my attention without good art, and there is a good reason for that.
People are visual. The more new, interesting, and unique content that you introduce, the more illustration is required to convey all that newness to the players in a way that they not only understand, but sticks in your imagination. Without all that rich illustration, you might as well stick to, well, 'lions, tigers, and bears'. (Oh my.) The more innovative your setting, the more illustration you need to support it. If you are doing stock elves, dwarves, and so forth, then not so much. People have already seen lots of illustration of that. They already no what you are talking about. You can skimp on the art if you've got alot of literary value to fire up the imagination (think Tolkien, Burroughs, Howard), but even then, before that's useful you have to get players (whose average attention span is about 15 seconds) to read all those pages (and they tend to go glassy eyed in the middle of the grappling rules). It's just alot easier to show them pictures. People understand pictures. Show them enough pictures of a 'Kreighstad', and then you won't have to explain it's the purple-striped six legged beast of burden with a tail like a sail and a face not even its mother could love every single time you use the word.
But, since you ask, here are the things that I would like to see in a setting:
a) India: It's the most complex culture on Earth, and probably the oldest, and completely ignored in most fantasy fiction. I would NOT like to see a cheap rip off of India as a setting, any more than I want a cheap rip off of Africa or Europe or Aztlan. Rather, I would like to see a deep understanding of India inform the setting. More inspiration and interpretation than mere one to one correspondances. Play "What if?" What if a similar baroque culture like the Etruscans had conquered Europe? What if Christianity never arose past an obscure sect? What if the Greeks had suffered under 1000 years of slavery to the Persians. Suppose the Aryans that conquered India had pulled a Gengis Khan 500 years before he was born, and conquered Europe rather than or inaddition to the subcontinent. Mix and mash. Ok, now that you've got some things simmering in the pot, pull out some alchemy and make a setting that is so unique that I won't be able to immediately recognize the sorts of questions that it arose from. If you can do something like that, I'd be really impressed. If I can say, 'This is Egypt, and this Greece, and this is the Mayans, and this is King Author's Britain, and this is the Italian city states circa the early Renaisance...', then forget about it. That was lame the first time I saw it. Rather, I want to say, "Well this country is sorta like Japan during the shogunate, but not really, because its also alot like medieval germany, except that the relgion owes alot to subsaharan africa, only not really."
b) Animism: I've yet to see a really integrated animistic world, where beings live in two worlds and the distinction between the seen and the unseen is hazy and things stumble in and out of both on an ordinary basis. Show me a world where every rock, every stream, every tree is alive and active in the world, and ordinary folks deal with it as reutinely as you deal with breathing, traffic jams, and long hours in the office. Show me some great mechanics about how it all works, like what happens when you cut down a tree, or sit on a rock, or urinate in a stream and tick someone off.
c) Religion: Religion is so freaking shallow in just about every published setting. You'd think that the citizens of most published game worlds were idiots. Where is the robust theology and philosophy? Who are the world's great thinkers and what did they believe? Give me something with as much meat as, if not a real religion, then at least 'The Book of the Righteous' or Bujold's 'Five Gods'
d) Ecology: This is one of those things where I think you have to either do it all the way, or not bother. But, if you took the big risk and did some serious brainstorming alternate ecologies, you could have a really big payoff. Of course, this would depend on alot of high quality illustration, and that (though its content) eats into your other sorts of content. You could spend a monster manual sized book on ecology, and have alot of players go, "Why am I buying 15 pages of illustrated cycad varieties, airborne mosses, and land corals? And whats with the 12 page listing of small largely non-offensive psuedo-crustaceans, amphibianoids, and theocodonts that don't even get full stat blocks?", and the rest going, "Huh?" But there are a few authors that have really got big dividends out of small investments in alien ecologies - works by Burroughs, Gerrold, Amy Thomson, and even Herbert's Dune depend partially on evoking an alien setting where the fauna and flora (or lack of them) are conspicous. India ties back into this too, because even the domesticated animals there are somewhat wierd and alien. Pull this off as well or better than Burroughs (too derivative), Gerrold (science falls apart under scrutiny), Thomson (frogs!?!?), or Herbert (literary jedi mind tricks), and I'll spend money on your setting.
e) Rules: Crunch is content too. Give me balanced well thought out rules that aren't geared primarily toward getting players to buy more toys for thier characters, but address major unaddressed or still clunky issues in the game in a solid manner - and here I'm thinking about simulationist things like crafting, macro-enconomics, professions, tiny and smaller creatures (housecats on down), children, weather simulation, disease and toxins, non-adventuring training, demographics, and play balance things like high level adventuring as a non-spellcaster. Throw in rules for mundane blessings and curses, astrology, dream walking, creating magic items as acts of skill, divine providence, sacrifices and sacred sites - and I'm there.
Or in other words, make the setting I've always been trying to make, only make it the way I've always wished I had the time to make it. Do my work for me, and I'll pay you. Do something inferior to what I could have done myself, and which already dances in my imagination quite nicely, and I'll glance through it, maybe steal ideas from it, but I'm not going to pay you money for it.