Your title said M4N E... hence the confusion. Yes, it is still worth upgrading to the x4 955 or 965 on the M2N-E... they are supported on your board. But be sure to check the fine print for the CPU you want.
The Phenom II x4 955/965 have this note: "Due to Bios ROM size limitation remove LAN PXE ROM and change Crashfree3 to Crashfree"
Also you want to update to the latest BIOS before changing the CPU.
Changing the CPU on that board can be an investment, because if you want to change the board later in a year or 2, your CPU will still be pretty good. And Black Edition x4's can be overclocked quite well with a simple multiplier bump.