Tom, I guess I am on a bit of a crusade and like tinkering with technology and music. You are absolutely correct in that Colossus is more than what one would need for live performances. In a studio one may notice the higher quality of a 2.5GB Bosendorfer Sampled Piano. In a Jazz Club a 70MB piano may well be enough. In fact, I am getting so old and frail that I can't tell the difference between someone hitting a bath tub or snare drum.....its real bad.
So I have no real justification other than its an exciting hobby for me. Now it is not to say that when people listen to me play they are overwhelmed by the quality of the sound (not my playing). This to keeps me going.
My current challenge is to make Colossus & Kontakt flawlessly accept program and bank changes. This will increase the quality over what I have been using for auto accompaniment (LiveSynth Pro and modified sYnerGi GS Wavetable).