I have actually been letting the ego just fluctuate and not focus on music lessons anymore. The smaller / shorter missions all give you better payouts - This is a tip I got from @thatcryptodave and it really seems to be increasing my rewards. It's also much more fun not being so fixated on Ego! apparent 20% is a sweet spot! I'm yet to push it up that high. I'm trying to stack for packs here but hey, I keep spending my starbits!