You don't make the same argument pivot yourself, but this is something that crosses my mind every time I read about SPDY too. All this stuff has been done before. It's not a new problem, and none of the old solutions caught on. What makes SPDY special?
Google makes SPDY special. If something is unquestionably useful but hasn't caught on, what you have is fundamentally a marketing problem. Google is the biggest marketing company on the Internet.
I mean, SPDY has some technical benefits of its own, but the biggest items in the "Pro" column are that it's an open spec and Google has thrown its weight behind it, even dogfooding it in their top sites and a major open-source project. This got people's attention, which previous efforts didn't really manage so well.
More specifically, because Google builds one of the most popular Web sites and one of the top browsers, they can break chicken-egg problems by JFDI. Things like SSL improvements, SPDY, SDCH, etc. have probably already paid for themselves.
It hasn't been done before. A single entity working to channel all of the web's traffic through a single cached pipeline and using a special protocol to do so is not SPDY. SPDY is a competitor to HTTP, it doesn't implicitly have to be used for caching or for proxying, and it shows some significant advantages when used on its one independent of those functions, warranting an expansion of its use on high traffic sites.
