I think you have the right to drive your car once in a while even to get groceries. In some States such as NJ, the MVC application will tell you that the car will be restricted to "shows and educational purposes only", however in the sumertime you see them driving everywhere. I am yet to see a QQ plate car being pulled over.
MD leaves what I call a "gray area" That said, I don't mean to start a battle of wits here, and I fully understand and believe that if a cop wants to give you a ticket he will, no matter what BUT, if you read in the Historic Plate Application (link below) it says and I quote: "I/We certify under oath that the vehicle will only be maintained for use in exhibitions, club activities, parades, tours, occasional transportation and similar uses
If you ask me, driving it to work once in a while will fall under "occasional transportation".
However, if you drive it to work a straight week because your primarily ride is down, you are using it for "general daily trasportation" which is the other part you signed under oath and said had no intention on doing
I/We further certify that this vehicle will not be used for general daily transportation or primarily for the transportation of passengers or property on highways
You signed a bonding contract and are supposed to abide by it. Ieven though it is YOUR car, you agreed to the restrictions in order to get cheaper registration with no inspection and cheaper insurance rates, and as said above wheter your insurance company cares or not how much ou drive it has no legal relevance in this case.
So, yes, if your car broke down and will be down for a length of time you should make other arrangements or risk getting a ticket and possibly loose your historic plate rights if sent to court.
Hope that helps you see a clearer picture