I think one thing to keep in mind related to Danny's last rebuild -- KG and Ray Allen were both in their early 30's and enough past their prime to be traded at a discount (fortunately they both proved to have plenty in the tank). If Danny was trading for the 26/27 year old RA and KG, he wouldn't have had the assets to acquire both of them.
If the C's are going for a young max salary star (Butler DMC, PG...), my opinion is that he better be a superstar (top 10) quality guy because acquiring him will drain our assets. Butler is good but not good enough IMO, so I wouldn't trade for him.