For as long as I have owned 911s there have been upgrades to the aircooled motors from various shops. Singer is not the first but it used to be that you took old cars and put newer engines and body kits on. Even V8 engines. Singer is just the first to do much of anything with the 962 and also part of a recent trend to make newer Porsche's look like 73 or older. 

I'm on the fence about their actual value. I would prefer an original 73. That said I would take that original engine and turn it into an MFI dual plug monster in a heartbeat. Maybe upgrade the MFI to something more modern but you get my point. I don't need to spend Singer money to have a fast old 911. Can still add coil over shocks etc.