I once (half a year ago actually) asked almost to death an AFIP office
Yes. it is legal. But you can not get out of the country with your own argentinian plated car, you will have a car for internal use only, AFIP will not allow you to cross border with argentinian car if you are a tourist (only citizens or permanent residents can do it). There is one exception for tourists - rented cars, if it is rented offcially you can cross border.
You can drive in and out of Argentina ANY other car (chilean plates, american plates etc) does not matter if it is yours or not.
Nobody cares about your visa, this question is for DNM, you should always show all the documents about the car, why are you permitted to drive this car, your driver licence and ID (any that you have, passport for ex). Inside Argentina you can drive any car, but as I said with argentinian car they will not let you out.
I don`t recommend it. They will tell whatever they want to sell a car. They do not decide nothing.
Fishmanfun, ask AFIP.