You can consider the EGT as an early warning system....normally in a turbo charged engine you see damaged heads coz of overheating caused by turbo, by the time that temperature shows on the conventional temp gauge on the stock instrument panel, the damage is already done. EGT will warn you a lot earlier, hence you will be able to bring down the temperature just by dropping the pressure on the accelerator pedal.
Boost which causes this temperature to go up can be controlled and kept in check if you have a boost gauge.....so I believe that pyrometer/EGT and a boost gauge is a must on any turbo charged vehicle even it it has a stock setup, specially when it is twenty years old.