Now, I remember reading this information somewhere, but I can’t find anywhere which has the information. I think some people have data for this since 1960 or something… If anyone can answer this, how many runs does the average home run, triple, double and single add to the team? Say, how many runs, in the periods where this type of stuff has been recorded, has the average double brought to the team of the player hitting it? And the same thing for the other hits and possibly walks?

Here’s one answer: http://www.tangotiger.net/lwbymob.htm

It varies specifically with the season, but roughly:
1B = 0.47
2B = 0.78
38 = 1.09
HR = 1.40
So, about 0.31 runs per base.  A walk is worth about 0.33 runs.