Thanks Chris. One of the problems is that I don't know if the aggregate was seeded or mixed. So, I don't know if it's full depth or just a surface application.
Either way, I will probably propose going over the existing slab. I don't usually like to do that, but the existing slab is 20 years old, 8" thick and doesn't even have a crack. The savings would be >$10,000.00.