That's a pretty good top 20. I'd rearrange a few of the names, and I'd add Jimmy McLarnin and Kid Gavilan (maybe I just missed them), but I don't see any major flaws.
My own top 10 would probably look something like this.
1. SR Robinson
2. Henry Armstrong
3. Muhammad Ali
4. Willie Pep
5. Joe Louis
6. Harry Greb
7. Joe Gans
8. Archie Moore
9. Benny Leonard
10. Roberto Duran
I'll probably have a different list by tomorrow. I add and remove fighters on a regular basis
Not in any particular order.
Ali
Foreman
Hopkins
Saddler
Liston
Frazier
Louis
Hearns
SR Leonard
Hagler
Mainly biased towards old-timers and heavyweights, but those are my favourite's.
Because Lennox avenged all of his losses, it could actually be argued he was the most dominant heavyweight in history, aside from Marciano. I have him at 4 on my own list, behind Ali, Louis, and Holmes.
It'll probably be the most financially successful fight. In 2014, they're really the only active fighters that people who don't follow boxing care about.
I doubt it will be more culturally significant than say, the first Ali-Frazier fight or the Louis-Schemling. I don't see it transcending the sport of boxing and become a huge cultural event like those fights did.