mac address can be changed with mac spoffing thats a simple hacking tool even possible in busybox
Yes but only temporary. Usually mac address is stored in a read-only type of memory, can't be edited...Yes you can use the mac to try track your phone. Calling the cops would be just a waste of time, invest that time in searching a nice program to import the mac and search your phone. You can also contact your carrier, they can also help you, if they want to normally 
"invest that time in searching a nice program" There is not such a magic program AFAIK.My carriers assistant confused MAC address with mac os. He is completely ignorant.
When I lost my phone I used my devices on google to locate it. Wasn't exact, but when I saw where it was, I knew exactly who had it.
But you were lucky enough that someone didn't turn off your device, and your GPS was open by default.