My ornamental gr is bare in the middle so what should I do?

Your thoughts are correct. Ornamental gres die in the middle when they are ready to be divided which can be as little as three years. You'll get that waterfall look back and you'll have a much larger "waterfall". Agree to share some with friends and family and if they come over and help you lift and divide it. It's a lot more physical than dividing daylillies or hostas!