Currently, the menu brought up by the Buffers menu item in the menu bar only shows the last 9 buffers and no more than about 29 characters of the buffer name. H
How 'bout buffers-menu-buffer-name-length and buffers-menu-max-size?
You may also prefer using C-mouse-1, which gives you a different kind of "buffers menu", which I personally prefer (so I just get rid of the "Buffers" menu with (define-key global-map [menu-bar buffer] nil), thus saving scarce menubar real-estate).