The difference I see is complacency includes apathy and passivity, a disconnect from ourselves and the world; while one can be very proactive and connected and passionate, and still be content. Complacency is a state of mind; contentment is a state of being.

I'm mostly content

To be content, you have also have to be complacent. Otherwise you'll fret yourself to death because nobody is perfect and nobody ever "does enough" to satisfy everyone. Better to just please yourself and not worry about it.

Good post. I am far from complacent, I am working hard to improve things every day.
Yet I am content in that. I have been in some bad places in my life, so now is pretty awesome.
I try hard to get others to find this contentment. I wish people would change, so many people visit or stay a while to get away from their lives, all say it is a real oasis, yet they leave and don't try and change their own spaces. I can be very unpopular in many circles pushing my changes.

I'm content but aware of defects and dangers.

A third option might be useful. Interested - self-aware and committed to continual learning.