Terry,
I just dealer traded an '04 XLT premium 4x4 with 32K miles (cloth seats, no Adrenaline, no moon roof) for $16K. Third-party sale would have been closer to $17.5K.
Your ST is a little high on mileage (not bad), but more decked out than mine. I would suspect the Edmunds prices to come out much higher than mine.
P.S.
I ran the numbers given what you said for options and my zipcode on Edmunds and got the following:
Trade-In: $17,882
Private Sale: $19,859
Dealer Retail: $21,661
Those seem reasonable to me.
TJR