"They might be indicative of the ratings a kid has, but I don't think they harbor any independent value that a person should look at when recruiting (FT percentage and possibly GPA notwithstanding)."
I think this is right. I think a coach would get into trouble signing players based on HS ppg, but I do think it is a useful filter method when searching for recruits. Looking closer at HS ppg has adjusted my thinking a little on what makes a good scorer. Over the last several seasons at Hood, I have placed a much higher value on LP and PER after looking closer at HS ppg. Previously, I would discount LP ratings in bigs in favor of ATH and focus on ATH, SPD, and BH in guards. I love ATH, and my teams have done well with lots of it, but I'm not sure that it impacts scoring as much as I previously thought.
As for spg, I have never had a good feel for exactly what goes into it. In looking at the Wooden DIII leaders in steals, DE doesn't seem to matter much. Here are the DE ratings for the top 10 in steals: 21, 49, 20, 30, 18, 25, 71, 50, 37, 21. Just eyeballing the numbers, it looks like they either have high SPD, a combination of ATH and SPD, or high ST plus some ATH and SPD.