457s are a two edged sword, they price Australian workers out but lower costs for consumers, and we are both. Restaurants can't afford to open on public holidays because by the time penalty rates are factored in, a nights trading will cost the owner money. They few that do open stick on a 20% surcharge making it unaffordable for many consumers.
It's unusual in many cities to find an Australian driving a taxi, Indian students who are happy with $10 an hour are the norm. Few people want to pay fares that would attract Aussie drivers.
If 457s could be used for restaurant staff you could eat out for less than half current prices but unemployment would increase.
There should be a levy paid for each 457 visa holder employed, that way companies could still fill positions where there are no qualified locals but an Australian would always be cheaper and it would be worth investing in training them.