I have a friend who was working on laying Tarmac at the car parks down Murray Street and appearently these car parks can be quite lucrative if people buy an individual car space and then rent if out. Don't know if this is the route St. Mirren are taking but would be worth looking into. I believe spaces go for upwards of £20k.
Here is a statement I've found on a website called Park First Investment...
Airport car parking is at a premium and has been a long-standing, high yielding corporate investment worldwide. Park First is proud that this investment is no longer just for the super rich, with individual parking spaces now available to purchase from just £20,000 each.
Single or multiple parking spaces are available to purchase, which provide a guaranteed return within the first two years of 8% per annum. Each parking space carries a single title deed, which is registered in your own name or that of your company at the Land Registry.
Glasgow Airport is expanding, along with all other main city airports. It offers strong long-term growth due to the massive expansion of global air travel. Glasgow Airport long stay parking is an excellent commercial property investment and a fantastic way to diversify your investment portfolio.