The SX650's pretty mundane and much newer/more chintzy in physical quality. I cannot imagine spending 150 smackers on a KR-5200, though -- unless maybe Echowars rehabb'ed it!
The four gangs and three filters refers to the FM circuitry; simply put, it's a more sophisticated design than, e.g., the Pioneer SX-650 - which I am pretty danged sure has a three-gang FM tuning capacitor - the benefits should be in terms of selectivity (ability to resolve stations). Kenwood was and presumably still is a radio company first and foremost; their tuners tend to be better than average.
As an aside: I didn't know that the 5200 had split power supplies (like the KA-7100, two sets of secondary windings in the PT, Echowars?) - that speaks well for its oompf relative to the SX-650.