For the 2013-2016 models, I actually think the lower level "Premium" trim on the BRZ (and its equivalent in the FRS) will hold up very well. The only issue with the higher level trims is that the spoiler is kind of a fiddly bit that just doesn't look very clean on the car. One of the reasons I got the lower level Premium trim level.
The only thing that I think is an issue I have with stock car are the rear tail lights. The weird silver/chrome reflecty bits are a bit distracting.
Here is my stock BRZ with clean lines. I think it will age very well indeed. If you have a bone-stock twin 25 years from now I think you will probably have something desirable as the younger kids who had one are bitten with the nostalgia bug. As usual, modded cars will not be as desirable.
