I don't think DR is considered one of the 4 big man skills. DR is a secondary skill for all players I believe. This is not saying that DR is unimportant, although playing with your back to the basket makes DR less important in my eyes.
I believe that the generally accepted 4 skills for big men are IS, ID, RB, and SB.
As far as shot-blocking goes, I believe in its value as much as I believe in the value of any skill. I don't think the game engine is set up to have 12 skills but only 11 of them of value. Is it cost-effective? That's a function of your team and the tactics you play.
Once I scored a basket that still makes me laugh.