Re: Shares are valued on expectations of future profits distributed as dividends, right?
Once upon a time, before tax laws made a hash of it, yes. These days, a decent dividend is more a sign of a moribund, government regulated monopoly/oligopoly than anything else. Stocks instead are bought and sold on the basis of how much you think you'll net when you sell it for capital gains. The overall negative effect this has had on the market, and its usefulness as an economic indicator is tremendous.
Of course, the safest estimate of that gain is a division of expected profit from selling widgets to the public divided by the number of shares, with a simultaneous examination of the sales growth trend for the company. Facebook doesn't make widgets so that first bit is right out the window, and now what we're hearing is that FB knew they were on a down slope for their "sales growth" proxy to boot.
So the end result of your analysis stands, albeit via a more circuitous route.