I don't think Turkoglu has any trade value at the moment, and with three more years under contract after this year he probably has negative trade value. So I don't see the Suns being able to move him for anyone, much less a big with an expiring contract.
However, the Suns could in theory trade Richardson for either Dalembert or Troy Murphy. I think both Sacramento and New Jersey would make this deal since neither player is being used much this season and Richardson's contract is expiring as well. Dalembert is now coming off the bench behind a rookie and Murphy is getting DNP's.
Imo, there is no way the Suns re-sign Richardson, so this is his last season with the Suns anyway. He has played well this season, but not consistently enough. And we have players on the bench who can take his spot so his loss can be overcome to some degree. Neither Dalembert nor Murphy would turn us into a championship contender, but I think it would make us more competitive this season.