I've heard getting the Key to the City is sometimes broken and I can't remember if it had to do with town or not but there are other rewards for doing things as a doctor.
According to the Prima Guide, you can receive:
Complete 3 inoculation jobs = Medical Trophy of Honor
Complete 10 Building Emergencies = Medical Trophy of Valor
Diagnose 40 Sims = Medal of Mending
Help 10 Sims in "Local Emergencies" = Tending Trinket
Reach Level 10 = Key to the City
Complete 5 Free Health Clinics at Level 10 = Skeletal Endowment
I know for a fact about the skeleton, 10 buildings and 40 sims but I'm not sure about the others. As for the notification you will receive, it will come as one of the in game messages in the top right corner of your screen. Then you'll have to send your Sim to City Hall. I don't know what happens if you miss it though.
This is fantastic! I have been experiencing great frustration regarding all those big empty lots in Moonlight Falls that I could do nothing about. Question: Since the rules have changed regarding this, can we make those changes in Edit Town now to an established dynasty?
I'm on the fence about how to answer this which means I'm going to defer to Metro's wisdom. I'm sure he'll check the thread by the morning and give his final answer.