I regularly take my old car to the monthly cruise in at SS. The reason the attendance was low last night was because the forecast was for rain. Most owners of classic cars don't want to be out in the rain. That is why I didn't participate. If the weather is dry, even in the summer months there are usually about 100 cars at the cruise in.
I believe if the rules were changed to accept cars 20 years or older there would be way too many cars showing up and being turned away, especially in the winter months. I think the max is about 256 cars.
I don't know what effect losing parking spots due the apartments around the square would do to the cruise in. I know it is very popular and neither of the other town squares could support nearly the same number of cars.