Does SPDY protocol eliminate the need for CSS sprites, combined JS and CSS files?
SPDY allows your browser to fetch all the images in parallel, which helps. If the browser has sufficient bandwidth, this can be enough to make SPDY unsprited as fast a HTTP with sprites.
But, sprites are still better for absolute performance.
Usually, when you combine 5-6 images the resulting size of the image is significantly smaller than the sum of the sizes of the individual images. Your results will vary, depending on what types of images you're using and how many there are. The css tricks guys have an example: http://css-tricks.com/css-sprites/
Even with the multiplexing of SPDY, cutting down on requests will likely result in performance boosts.
Don't use CSS sprites with external stylesheets - Resources in external stylesheets are obviously only discovered after the external stylesheet has been downloaded, and only once the rule matches an element. The advantage they provide of reducing HTTP requests is unnecessary with SPDY due to its multiplexing. Therefore, CSS sprites just make it slower.