There is one that is not too far from us that appears to have been turned into a construction company's office and with overhead doors on the bays has storage. I'm not sure why it closed because it is the only one in the area and now people will have to drive a bit to wash their car.
In my area I am seeing a lot of commercial store front buildings being put up. Small companies like plumbers, heating and cooling etc rent small spaces that have a office and small area for their inventories. 1 to 2 bay would be all the space they require. They seem to fill up as fast as they are built. It would be easy to convert the bays for this type of store front and since most car washes are already zoned commercial minimum city approval would be required.
A tandem 4 bay here in our small city was converted to an oil change lube ... a bit like Jiffy Lube but not franchised. I remember when the car wash was first built & supposedly such fabulous innovation such as the ability to see out of the adjacent equipment via one-way glass. The customers could not see in though. I am not sure if that one way viewing innovation is still there or if they took it out.
A local large multiple screen movie theater is using another one as an expansion of their parking lot after it was demolished.
I've seen them turned into detail shops, lube centers, safety/emission inspection stations, mechanic shops, tint/alarm/car audio shops, almost always something car-related. Sometimes they add a building on the end for a customer waiting room, sometimes they close up another bay for that. Seems like a lot of the detailers just service car dealers and don't need an office.