I have a 2004 t-bird. How necessary is power steering flush, fuel injection service and/or throttle body service? If not now, when?

Agreed. Usually, a PS flush isn't necessary unless the system has been contaminated or the fluid is worn out - 80K is about right. Fuel injection service - not needed - RARELY needed. Throttle Body Service/Cleaning is seldom necessary and usually only after a major service with a lot of miles accumulated. The Idea of cleaning the Throttle Body is to improve idle quality. Keep the Oil changed and the fuel fresh - check the quality of your antifreeze.