Pays off student debt - university fees to become a doctor in Ontario are very high. Pays off staff and office expenses. See cuts in fees from Ontario government, higher taxes from both feds and provinces.
I think your $500,000  is generous considering everything. Gets a small business deduction on ACTIVE business income only. 
Corporation cannot buy homes, boats, cars etc. Money has to be taken out of the corporation and is now subject to personal taxes. The fact they are dividends  does not make them tax free. He/she will probably have to pay additional taxes as the dividend tax credit only covers a proportion of the dividend income.

BTW since when are doctors the super rich ?