So specifically on assists, I think the benchmark is points per unassisted possession.  If points per possession are 1.06, then let's say, for purposes of discussion, that points per unassisted possession are 0.7.  Without any assist, we can let some guy go one on one and we'll get some points anyway, so the value of the assist is the difference between assisted and unassisted points per possession.

An assist means we get 2.2 points on the possession, so the baseline value of an assist is 2.2 - 0.7, or 1.5.

But passing to James Jones for an open 3 pointer, or to Roy for a contested driving layup, doesn't really mean I earned my team all of those extra points.  I'm depending on the exceptional skill of those players to convert -- it isn't my skill that generated all of those points.  If I pass to an open Aldridge off the pick and roll for a slam, it really is my skill that did it.  So on average, we recognize that some assists are helped assists (helped by the skill of the convertor), and therefore on average the value of assists is not as high as pure point differential would reflect.

No one thinks every blocked shot is worth two points.  It is only worth the points that the opponent would have had on the shot, and not all blocked shots would have gone in -- and since sometimes the opponents retain possession and score, that has to be factored in as well.  But a retained possession has less time on the shot clock, which makes that possession less likely to result in a score, so we don't want to overvalue retained possessions, either.  And with multiple blocked shots, there is the continuing intimidation impact.  A player's first blocked shot in a game is of less value than his third, because by the third, people start to think about him on shots he doesn't block.

I'll try to write more later, but work may overtake me today.  If I forget, and you want to discuss it more, perhaps another diary, since this one is receding so rapidly.