i'd argue that the main reason they were interested in nuclear warhead AAM's at the time was the lack of reliable guidance systems for missiles. so long as you could set the timer and course right before firing, the big AOE on a nuclear blast would be likely to down a bomber, even if the missile itself didn't come anywhere close to hitting. as soon as they got guidance systems that could reliably track and hit targets, the use of nuclear warhead anti-aircraft missiles stopped in the west. (the soviets kept at it a little longer, but given how their electronics tech tended to lag behind america/NATO, it's not surprising they'd want to retain the option. they mostly focused on ground launched nuclear SAM's though)