I'd add this:
I read something interesting: It is not reaching the goal, it is who you become in the process of reaching that goal.
It is always fun to have a few pieces in the works which you can learn easily and just play. But, I think the real progress comes in having a couple of "big" pieces which really stretch you as a musician.
I'm currently working on a Beethoven sonata, as I mentioned earlier, and it is a killer...there are challenges of fingering, just basic note reading, dynamics, precision, etc. but when I learn this piece to my teacher's satisfaction I will be a better musician because this is a stretch piece for me.