Can you share the load time that you got before and after working on those technical parameters? In our website, we usually use the webmaster tools and at the same time compare it to our competitor. For example we are in the hotel business so we try to compare our site performance to the biggest hotel chains.
But then in my opinion once you worked on those technical parameters, there are still other aspect of your site that you need to check to increase the load performance.
1. Check the size of your page. Initially, our site loads around 10 secs and this is because of our layout and we use a lot of images. First step is we compress all our jpgs without degrading the quality of it. The second part is a reconstruct the layout or our scripts to reduce the DOM elements in our site. I notice a difference on the load time when our DOM elements is less than 1000
2. For sprite images. It will be better to create a sprite image upon development instead of spriting them on the fly which is why I think they said that it is a waste of resources. I use this site for spriting our images. http://spritegen.website-performance.org/
3. You need to minify and combined all your css and javascript.
I also follow all those rules in YSLOW and Page Speed and I can see a significant improvement in our page load time. Without using a CDN our site now loads around 4-5 secs and with CDN, I think around 3-4 secs.