CP3 will be available at the trade deadline this season and possibly D12 as well. Amare will be 29 in November and Melo just turned 27. They are certainly in the early stages of their prime years with many (injuries aside) years to come. Getting a CP3 or D12 in February or next summer affords them years of prime to play together and years to acquire role players. Again, role players are easy to acquire but superstars are not. Further, role players will flock to the Mecca to play with a core like that.
P.S. KG and Allen were 31 when they arrived so Amare, Melo, CP3/D12 will all be younger. That said, they did win a ring and have been dominate for years. I'll take that considering we have not won since the early 70's of have been dreadful for the last 10 years.