I would find it really useful if there was a keyboard shortcut (such as CMD+Up / CMD+Dn) to iterate through the note styles so you don’t have to right-click the menu each time. Alternatively (or additionally?) I am far more likely to use existing note styles that I’ve created rather than tweak a note each time, so perhaps in the “note style” tab of the inspector it should instead list all your created styles so you can just click on a style to apply it straight away and then have “create a new style” and “edit style” buttons to show what’s currently on the “note style” tab.
How about using a keyboard shortcut for the style itself? That strikes me as more useful than browsing through styles (more often you’d know what you want), and direct shortcuts can already be assigned via the OS X keyboard system preference pane.
That actually wouldn’t work because the system reserves Shift-Cmd-3 & 4 for screenshots. Ctrl-# is a pretty good set. I use that in a number of programs since nothing on a Mac ever seems to use those.
Perhaps something like CMD+SHIFT+1 > CMD+SHIFT+0?