The main result is that most of the benefit comes from putting everything through one TCP pipe. This, of course, only works if almost everything on a site comes from one host. This is a good assumption for Google sites, which communicate only with the mothership. It's not for most non-Google sites.
Looking at the facts, it seems pretty obvious that whatever theoretical gains you can get in select scenarios with SPDY, this super-minor gain is not worth it compared to the associated complexity cost.
Not to mention I don't like the idea of Google now not only running the worlds tracking units, the worlds most popular browser and most popular websites, but now also dictating internet-protocols without taking input from other parties.
Also, this is not part of a big, evil Google master plan. The engineers who developed it are well known and they presumably tried to do their best from a technical point of view.
For most optimised HTTP/1.x sites there's already a complexity cost of merging JS files, merging CSS files building sprites - including the tradeoff of getting the bundles right, which of course reduces cachability.
If you are revving your bundles with hashes (main.8a4ce55.js), caching shouldn't be a problem. Not sure what your build process is, but there are plugins to do this on most setups.
When two separate resources together at build time they're being coupled from a caching point of view if one gets changed and the other doesn't they they both have to be re-downloaded because the bundle has changed.
And all of this is a build-time problem.
If we're going to engineer the HTTP-protocol to solve build-tooling and development related problems, we might as well add JS-linting and minifying to HTTP itself as well.
Seriously: This problem is best solved elsewhere.
Just testing SPDY on a site I was building last year, it seemed to provide double digit speedups. Not bad for my effort of typing SPDY into nginx.conf.
So yeah, I dislike Google. I use FF and disconnect search. I hate Google's intrusiveness and anti privacy stance. But at least SPDY provides actual benefits today, versus complaining about standards.