OK… if the thermostat was corroded, or beginning to stick that $80 bucks just saved you about $2000, wich is the cost of a new engine, which is what you would have needed if the thermostat sezied closed and you did not catch it immediately. Alluminum block engines have NO tolerance for excessive heat. Your entire block would have been fracked.
The fuel filter is a good thing to change, pretty inexpensive, and you will probably notice an increase in performace.
Tranny flush is ESSENTIAL, and should be done more often than 100,000. Tranny fluid needs changed from time to time It gets hot too and suffers thermal breakdown, just not as fast as motor oil. And it also picks up metal dust as your fears wear, and teh metal dust abraids the gears making the gears wear faster.
Plugs, should be changed from tiem to time. If the tips foul, you lose both performance and gas mileage. Plug wires also break down over time. Both are pretty cheap to fix, even with high-grade components.
You WERE overbilled on the labor charge. You could ahve gotten the same service for less at a private shop. Also dealership plug wires tend to be very over-priced (I was once charged $160 for 4 plug wires at a Ford Dealership, the wires slagged out 3 weeks later… I got my money back).
For the services you list, the bill should ahve been in the high $200’s (plus the thermostat) at a non-dealership garage. So, about an extra $125 for having it done wherever you had it done.
(yes, I spend a LOT of time in car repair shops, they are my primary customer base)