Well Dustin, the 1961 Topps Sporting News all-stars are indeed a cool-looking assemblage of the game's best at that moment. The dazzling design was the company's best effort among their all-star subsets over the years, though they were all usually beautiful. For 1961, Topps seemed to select stellar photos of the stars. They all have a slightly dark appearance, with a dark background, creating a nice contrast to the strong white newspaper backdrop.
You specifically mention the Willie Mays all-star, and this is simply one of the most gratifying of all Say Hey cards. What a glowing smile! Looks "a million times" more attractive than Willie's regular Topps card, where his surly countenance is revolting, at best.
As far as rarity, which refers mostly to what exists today, or what survived over the years, I would urge you to consult PSA's population report. It will provide you with a good idea of what the most significant and important third party authenticator has handled in their nearly 25 years of existence. Since you seem to be enthused to build this subset, get on eBay and look at what is available today. Prominent dealers will have a nice selection for you to choose from.
The '61 high numbers are not frighteningly rare, but in ultra high PSA grade, they can be very, very tough. Furthermore, there's lots of competition for them, particularly if the specimen is well-centered to perfectly-centered. The gents who are vying for a respectable position on the PSA 1961 Topps Set Registry have their sights zeroed in on ANY high-grade specimens they still need. Two names come to my mind that are ferociously tough and you will have to face down the most wicked auction dogfight of your life should a PSA 9 MINT come on the block---Jim Gentile and Bob Cerv. The fact they're both exquisite-looking cards compounds the situation. Same would also go for PSA 8 examples of those guys that are centered. Oh brother. A third name came to my mind of a genuine toughie--young Yanks' pitcher Rollie Sheldon.
Fellow collectors, please correct me if my memory has become toasted on the Topps '61 high numbers, for the benefit of Justin, myself, and anyone else who may be pausing to read this thread.
Cheers.
---Brian Powell