I'm all about honesty, and honestly, the intro is a little short if you're going to make a 30 minute piece. Don't get me wrong, i like it.
1.) Try bring in some strings (softly) around the :50 mark, but make sure they dont overpower the piano, from what I gather you want the piano to be the main theme in said piece.
2.) Play with octaves. Up down left right no matter the case a higher and/or lower octave helps to break the monotony even if you use the same notes.
3.) Light drums as well help to break away from monotony without overpowering the piano. Just make sure that you keep focusing on the piano / melody. If you focus too much on drums you can lose your train of thought.
4.) In order to keep people listening for 30 minutes you have to "make" them listen. Bring in some parts to pump up the listener, then tone it down a notch, make them think "uh, i wanna hear that again" you can buy yourself some much needed "interest" from the listener.
All in all this isn't a bad into at all!