I can see the point of making it user updateable for the average user, so why not do the heavy lifting in the configuration settings app. What I mean is, store the images (emoticons and the like) separately just like they are now, but put an option in config to update image sprites. Then you build the sprite from the new images the user has put out.
This gives us the best of both sides, easy to customize, but also still give the performance of sprites.
I see this post is in the Komento forum, but the same idea holds true for Easyblog which is the product I use, and as those have stated above I'm a little frustrated that sprites aren't used for many of the images.
Just my 2 cents
Don