I have to sell almost 20 square bales to earn enough profit for 1 rake teeth on my rotary rake. I'd have to see 2500 or more to have profit enough to replace the cam track and followers.
I set my rake so it doesn't do tillage work and yes it leaves some hay in our rough fields. I think it leaves about 1-3 square bales per acre. The wheel rake guys don't leave much behind but our little fields don't have much for straightaways.