Re: who writes down the MAC address of their device?
Answer: anyone who uses static DHCP leases on their network. I have a perfect audit trail of all MAC addresses of my devices going back 15 years.
In any case, if memory serves me right iThings will use a randomized MAC when scanning, but not when connecting to a known network.
As far as the idea goes, I used to run a similar MAC trap and Bluetooth (in the 2000-es Nokia used to ship with Bluetooth visibility enabled) for years. Initially (~2008) it worked quite well (especially the Bluetooth portion). I turned it off last year - it stopped logging anything meaningful. Randomized MACs and Bluetooth being invisible and/or inactive by default in Android/iOS did with that idea.