Base64 URL might prevent extra requests, but it also significantly increases the size of the images involved, so the performance benefits of having one fewer request may be outweighed by the extra weight in the total download size
Reducing the number of requests may be a good idea, but it's not the only factor involved in your site's performance. In fact, for most sites it's probably relatively low down the list.
In addition, if the images or your CSS ever change, then having them all in a single file actually works against you for people who have already visited your site, because the whole thing will have to be thrown out of the cache and reloaded. If they were separate files, only one of them would need to be reloaded when it changes. Again, you're increasing the total amount of downloading required.
Don't try to optimise blindly; Use a site performance analysis tool to work out where your specific bottlenecks are and fix the most important ones first.