I object to the premise of the question...somewhat. The fact you have so many CSS files speaks to unnecessary bloat. You are probably coupling your styles to a specific context rather than to classes of content. Check out what they are doing at Yahoo for what I mean.
When your CSS is less-context specific, it becomes leaner. This then dramatically reduces the size of your files and mitigates your issue by curing the disease rather than treating the symptom.
So take the time to rethink your CSS to make sure it is only as big as it needs to be. Then organize your layout according just to whatever makes sense for you. After all, the layout of your CSS into multiple files is for your benefit only as a developer. The files will be minified and combined into a single file for the purposes of caching and performance.
And CSS files that are less likely to change because they have been designed for maximum immutability are ideal for caching.