Ehh, I'm not big on this argument really. You have the right idea that Show/big name celebrities will draw, but this was Show/Cena/Punk and it wasn't even the main match on the card so I feel like it didn't make all that much of a difference because it's not like him being in the match is going to generate any kind of interest compared to if it was him/Mayweather, Shaq, etc. I don't think Show helped how many buys 2012 got, but I also really doubt that triple threat as a whole really got any, it may have been a final selling point on some people that wanted to watch HHH/Lesnar but didn't want to spend the money unless the rest of the card was pretty good too.
I will label it as a good secondary main event that seals buying the ppv.
Punk/Brock and Cena/Bryan really don't stand out from one another, and not because of Cena or Brock. Yes Punk and Bryan worked great matches but they aren't special. Its the same thing with Orton as champ, its never worked because people don't buy into these guys. That's why Punks 400 day reign was essentially as a midcard act until he faced Rock with Cena in the main events of Raw and ppv to sell them.
SummerSlam would've did better numbers with Cena/Brock and Bryan/Punk in the secondary role because the fact is while the arena buzzes for Punk and Bryan, wallets only pop all the way open for Cena, Brock, Taker, Rock, Trips, and Dave in recent years.
Its like Mayweather's fight. People pay to watch Floyd, love him or hate him, same with Cena because they are an enigma. Mayweather vs Canelo sells better than Mayweather vs Garcia/Lucas despite it being known the latter two are technically (much like Bryan and Punk in a ring) better fighters than Canelo, but lack his it factor. No matter how much better guys like Bryan, Punk, and Dolph are in that ring than most it means jack to they touch that box office and keep them channels from flipping ... Which is why we will always have part timers and HHH talking 20 plus minutes