Honestly, having only bought the 3rd or 4th generation upgrades in each room, I've managed to make masters in all 3 rooms before the peeps turned 60 rather consistently. In a few cases, with hardworking peeps, even before 55. Either I've gotten lucky or I'm a brutal taskmaster (possible?), but I really have no interest in shelling out the rest of the money for other career room upgrades.

I'll only buy those much later when I've got oodles of coins and nothing left to spend them on haha. Because, I really don't see why I should waste that many coins when the peeps really don't seem to need the career upgrades.

It's much cheaper to just pay 1100 to advance them/give them a head start and let them go at it that way.