Photo-etched parts add a level of realism hard to reproduce in injection-moulding.
M7y first "real" photo-etched attempt was on the Dragon Nashorn (not the new release). I got a set of photo-etched frets and cannot believe how they make a model look so much better and so much more professional.
Plus, the really nice part of using PE fenders and so forth is that you can get some great bends into the material, making weathering and damage that much easier ot model.
I too am hooked on PE, and that is a BAD thing, especially on my modeling budget...
Now add the turned-aluminum barrels and the Fruisil-thingy metal tracks and even that old low-two-digit-model-number-Tamiya-kit can look like a museum piece of you get it right!
[Remember, though, that photo-etched parts need to have a good primer on them before they will hold a good final finish, in a lot of cases.]