Santo did seem to benefit alot from Wrigley. But what if we tried to estimate only his value in road games? Doing a quick calculation to find his road OBP & SLG from 1960-73, I got .346 & .413. Does not sound that great. But in his time, it was pretty valuable. Here is the relationship from regression analysis between runs per game and OBP & SLG:
R/G =16.55*OBP + 10.56*SLG - 5.15
A team with an OBP of .342 and an SLG of .413 would score 4.93 R/G. The league average in those years was about 4.06. That would give us a Pythagorean pct of .596. Pretty darn good.
I also ran a regression with winning pct being the dependent variable and runs per game and opponents runs per game being the independent variables. Here is the equation
Pct = .515 + .111*RG - .114*ORG
If a team scored 4.93 runs per game and allowed 4.06 per game, they would have a .596 pct. That is how good Santo was just in road games.