I know that I can assign keyboard shortcuts via System Preferences, and those often even work as expected (maybe OS X is better now than it was).
However, I would love to see the ability to remove existing shortcuts so that I can assign them to the menu commands of my choosing. On that eventual day when I want to import an entire mailbox (normally I just drag individual emails to the sorter), I will not recall the menu shortcut - I simply do not use that feature enough to memorize a shortcut. However, to me, “⌃⌥⌘M” makes the best sense for a new Markdown note (so similar to “⌃⌥⌘N” for a new plain-text note) which I do use frequently.
BBEdit has the best implementation of this feature that I’ve seen (BBEdit also allows you to hide menu items and entire menus, which I am not specifically requesting here).
