if you drop your car over 1", aftermarket Performance shocks are highly recommended.
since the tein s-techs give an all around drop of 1.5"..i would definatly look into getting shocks (such as the kyb agx adjustables).
stock shocks last an average of only about 1 year before they give out...so save some $$ and do it all at once.
So with just the TRD springs that give you a 1" drop would be safe for over a year on stock shocks? Because the shocks are really over-priced here for the shock & spring set by TRD.
it depends. 1 year is just an average. you have an '03 celica so you should have relatively low mileage on your cars and your stock shocks should still be in good condition (depends on roads and how you drive your car, obviously).
AS A RULE OF THUMB, the lower a spring drops your car the stiffer the spring rate is. a stiffer spring rate puts added strain on your shocks and will make them wear out faster.
so saying a 1" drop is better than a 1.5" drop is better than a 2" drop and so on...based on shock wear. as already mentioned your stock shocks will go out one day, even on your stock springs. just whenever you get a spring with a higher spring rate, it will speed up that wear.