I do have to say that you got a pretty good rate. I understand that you have two rentals. That means that after the first rental you will have to go back to Hertz to return the car you have a rent a new one. Now, the agent may be able to put the same van on your new contract but there might be an occurance where the agent has to give you a different vehicle (mainly because the vehicle may need to be serviced... such as an oil change, etc). In the case of the van needing an oil change, the agent cannot assign your van onto the new contract.

Your best bet is to shop around and see what prices you come up with for 17 days. Call MIA, maybe they can find you a better rate. Plus, do you really want to take time in the middle of your vacation to go back to Hertz? MIA can get really busy and you can be there for hours.