dvs_03GT,
I like the stock brakes a lot. If you have them in good shape they are more than suficient for every day use. Plus for me it was necessary to keep them because of the 16" snow tires.
Now, if you would take your stang and go "road course racing", the brakes would definitely not be sufficient any more.
The only upgrade in my opinion is the cobra brake kit. It is cheap and proven to last. But that's only my opinion.