I would definitely not trade Dickey for the reasons you mentioned. I think you should move Buehrle though and take the 12-15 million in savings. Although he has been very consistent in his career I believe he's declining and next season won't look pretty. His BB, K and GB numbers this year have take a turn from his career and the velocity decline won't help.
I think you move him now and get the value while you can. Since we have depth in the rotation I think we can afford to lose him.