Now that the Fetchlands are in the Khans of Tarkir (KTK) block we know that KTK will be a "money" block like Zendikar: you can open packs for specific cards that are worth a lot of money and not care much for the rest of the set, and you can buy sealed product and set it aside hoping to sell it at a much higher value 5 to 6 years down the road.
If you had done that for Innistrad set and Zendikar set, you would have gotten a pretty good return. It looks like this will be the case for the Khans of Tarkir set, even if all of the other cards in KTK are not as valuable as the Fetchlands. The Fetchlands are the Fetchlands, what else can be said?
There will be A LOT of speculation on KTK booster boxes, and this is as expected. The question for a speculator is: do you buy a booster box and pull Fetchlands from it, or do you buy singles? This is what we know now:
1. The allied Fetchlands in KTK are already Legacy staples. They are MONEY, period. Never mind what future additional value they could get from playing a major role in future Modern competitive decks.
2. A case of KTK will sell for more than a case of Theros (that's for sure!). Say you pay $550 and you pull 4 fetchlands per box. That is a little less than $23 per Fetchland. Yes, there are a bunch of other cards you will pull that you can sell. Say you can pull an additional $50 in cards from each box (singles and common/uncommon playsets), that then reduces what you spent for the Fetchlands to $250, and the cost per Fetchland to $10.40.
3. If a month after drafting of KTK the Fetchlands are at $10, singles are better than the case, and you don't have to spend countless hours opening packs, arranging product, and selling it as dozens of lots to recoup the non-Fetchland value in the case.
Everything changes if KTK contains a valuable common card like Delver of Secrets, or a valuable uncommon like Unburial Rites, or a valuable rare like Snapcaster Mage. Then the case is way better than buying Fetchland singles, because you will get a ton of value out of the non-Fetchlands. I am not betting on it because KTK is a three-color set. KTK has a bunch of cards with three colors in the casting cost...... ouch, that is the very definition of Modern unplayable, and let's not even go into Legacy and Vintage playability.
KTK is a God-send for the casual budget player: I can pretty much skip KTK and instead benefit from how much cheaper Theros block packs will be in the near future. The scry-lands are casual awesomeness, and with how awesome awesome Devotion is, I don't even need dual lands to build a bunch of fun casual cheap decks.