When I was selling this gear back in the 70s, the most productive salesmen always evaluated any new gear that came in. These guys knew what would sell and quickly decided what they would steer their customers to.
The phrase was, "Knobs, Lights, and Meters". In that order.
The reality was that multicolored displays and meters - anything with motion, actually, did the job to convince a customer to buy one item over another. Now known as the bling factor, the analog VU meter pretty much still defines what folks remember.
Just look at how many amps McIntosh has today in its line up. For me, they pretty much defined the classic audio component look and have managed to keep it up for over 50 years. I think this is one reason why the 70s vintage gear is still popular, too.
BTW, I think Sansui was the brand that most understood the bling factor in the 70s with Sony being the most boring. The thing is that Sony was right in there with the sonics but catered to the customer who didn't want his stereo to be front-and-center in the house.
Cheers,
David