from carfax saying the dealer wants to buy my car and says's they'll give me $11,500 for it.

I just did a quick search on KSL for cars 2 years older through 2 years newer than mine, and for miles 20k under and 20k over mine.

There were four results:
2 years newer, 20k less miles: $28,500
1 year newer, 7k less miles: $19,600
1 year older, 5k less miles: $16,000
1 year older, 10k more miles: $16,800

Trading in definitely is not the best option if you're looking to change vehicles...