what do you want to do with it? i would sit down and think about what, realistically, you would use the extra space for. planning on using it for live performances? think about all of the things you need to do to get your songs to play, figure out if you can pull it off on just the LaunchKey. want to use it in your music-making process? map out what knobs you would /actually/ use a lot.

i've got a 49-key midi keyboard (Akai MPK49), which comes with a bunch of pads and knobs. i LOVE mine, but i don't use the knobs nearly as much as i expected. i mainly use it for fiddling around and coming up with ideas -- if i were to do it again, i would rather have a 61-key keyboard without buttons/knobs, and then buy a Novation LaunchControl or something when i start doing performances. plus, that separation might let you have the keyboard routed to 1 synth, while the LaunchControl is affecting the drums, stuff like that.