I don't see how it would be more comfortable than how it already is...
As a matter of fact, if this was added again to Messenger Plus! then you would also either need to click 3 times or you would either need to navigate thru the menu/sub-menus. This because the 'Edit notes' menu item would be a sub-item of 'Messenger Plus! Features' menu item.
As said, simple right click the contact, click 'Edit Contact', and click on 'Notes'.
Or learn to use the shortcut keys: right click the contact, press <E>, press <Alt><N> (for the English version)
Can't be more easier than that.
I use it all the time...
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