To help in your decision:
I recently traded in my perfect condition 06 4.4. I was 2nd owner. 70k miles and flawless condition.

I got 15k on the trade after some negotiation. Other dealers were in the $11 to $12 range, and higher selling price on the new car that I ended up getting for 3% under invoice. I felt I ended up with a fair deal. Kbb was suggesting $16.5 but I think that was high. In my opinion they seem to lag the current market by 4 months or so.

The dealer then sold my old X to a local used Eurocar specialist. They have it on their lot for around $20k. They've had it now for a little over a month. They are located in the northeast.

That X was a great car. Very few issues during the 6 years I had it. I kept on top of the maintenance and was lucky to keep the cosmetics flawless.

Good luck with your X. My experience says great car. I'm looking forward to my next one in a few years.

Ches