ya overloading workers will reduce quality, and ya you basically consumed the current content for now. Right now I am adding more systems into the game but soon I will add more rooms and Large games which are going to come with some added challenges. Eventually AAA which I plan to make you use multiple studios for but still a ways away from that point yet :)
Training endurance will reduce the workload costs.
I am really glad you enjoyed what I have already done I honestly have a lot planned and I hope you check out the new content in the future if you have the time.