Seems like these cars love to dirty up the coolant with rust and clog the heater cores.
I wonder if adding one of the many anti rust additives would solve this common issue?
I don't believe in additives. I believe in maintenance. If you change the coolant (which is often overlooked) and flush the system at its specified intervals, you should be good to go.
Often times the coolant system gets overlooked, many people just keep adding without realizing that their coolant is rotting away their water pump.
If I remember correctly the coolant retains metal through an effect called electrolysis, and this contributes to the rust.
Changing the coolant regularly and keeping it clean, and using a radiator plug magnet can increase the longevity of your cooling system. These "Stop Rust" things tend to clog up your cooling system. I have yet to see these things work.
You should also use a flush out every time you change your coolant. This removes any calcium build up which tends to clog the heater core. This is due to tap water calcifying due to it being boiled. If you use nothing but Distilled water and coolant typically the calcification doesn't occur as rapidly. However I've still seen it happen.