This is not such a silly question if it gets you to think about a couple of important things.
I would encourage you to look into what your Mustangs are really worth....try the Old Cars (magazine) price guide available at news stands. condition is everything so read the descriptions. The reason I would encourage you to do this is that it might get you to thinking about insurance you might not have worried with back when you bought the cars. I have a muscle car that I am pretty sure I could not afford to buy again today. Muscle car values have gone nuts...and some are just plain unaffordable for most of us now.
Same for the shop.....think about *replacement value*. I have lots of tooling that I bought surplus over a long period of time at bargain prices. I could not replace it in some cases as it may be old stuff that you would not find used again for a long time. It took years of shopping to find the stuff the first time and you may not ever find some of it again. Other stuff is still available as a new replacement....but at a price that is *many* times what I got it for. If your shop burnt, you might be hard pressed to replace some of this stuff without buying new. Most homeowner's policies have limits on specific types of things like tools, guns, jewelry. If you own more than that (again think what it would actually cost to replace), you might be SOL.
The thing that sticks in my mind is the Bridgeport mill I bought a couple of years ago, used. It had a Newall DRO and I paid probably the upper end of the going rate at the time. I have a lot of time spent rebuilding it and rescraping. I could not buy one in its current condition for even close to what I paid then, today. Additionally, I would not want to have to buy another that needed rebuilt, after a fire and spend another year or two working on it. So....what does it realistically cost to replace now and how much of my tool insurance limits does it eat up by itself? Probably time to put pencil to paper and do a real inventory of tooling and figure out if its time for an insurance rider for the shop.