Well, I've been kind of asking myself the same question about "Unsent", but could not think of a better name to convey that it's not just drafts, but also outgoing messages.
Typically, mail clients have a special local mailbox called "Outgoing" or "Unsent" or similar that gets used as temporary storage for messages that are queued to be sent but have not yet been delivered. In this system, Drafts gets used only for messages that people are still writing but don't yet want to be sent, where as Unsent gets used for messages that people have actually clicked "Send" on. By combining Drafts and Unsent, this important distinction gets lost - I'd be horrified if any if the messages in my Drafts folder were actually delivered.
Anyway, back to the original topic - a nice, possibly simple improvement would be to just not display the square brackets around the special folders: Rather than "[ Sent Messages ]" just show "Sent Messages", or even just "Sent" (since people already know that these mailboxes contain messages, making the "Messages" part somewhat redundant).
My suggestion would be to just display the name of the remote folder being sync'ed in that role, rather than the special name - this would let users name it whatever they want.
+1 for this, in any case.