I think you should narrow down the selection of fonts. All the different styles detracts from a cohesive result. The overall design looks clean and easy to look at, though.
Thank you for the critique. May I ask a few clarifying questions?
1. The goal of the menu design, aside from usability of course, is verisimilitude. So with the stamp, and the "PAR AVION," I'm striving to copy the actual usage of those two items. Do these add to the muddle? Would it help if I blurred the letters on those items somewhat so that they were more easily identifiable as mere design elements, and not text that's relevant to using the menu?
2. The Music/Speech volume labels were intended to mimic handwriting as one might see on the outside of an envelope. Of course, it's hard to find a handwriting font that is both legible and doesn't look like it was created by a computer. This idea might not work anyway, as the presence of the sliders definitively distinguish the labels as something other than writing on an envelope. Should I carry over the font from the left hand menu for these labels?
3. Do you count the "Back to Game" button as part of the "different styles"? Would it be improved by adding the beveling / shadow that the other buttons have (otherwise, it's the same typeface)? My goal here was to make an easily identifiable "get me out of this menu" button, but perhaps the difference in color is enough?
4. How cohesive do you think I should be across my other standard/out-of-game GUIs (RestoreY/N, Save, etc.)? I'm currently trying to decide whether to keep the airmail envelope as a defining design element across the board, or whether I could use other ephemera (luggage labels, tickets, etc.) so long as I kept the same color scheme and typography.