[SMCARA] To upgrade my Rig or not

[Tom Shelton, ND3N]

Hello fellow radio guys.  I need your advise.  
I'm thinking about selling my TS-590S and getting a TS-590SG.  My questions are: How much better is the SG  over the S, and what should I ask for the S?
Is there another rig in the $1,600 to $1,800 range I should consider other than the 590SG? 
Tom Shelton, ND3N240-434-3811
If it ain't broke,  let's fix it until it is...