Ned Macey at Football Outsiders wrote an article about the NFC North. He discussed the Randy Moss rumors and brought up that Moss might not every be great again.
As Macey says in the article, it is impossible to compare Moss to most WRs because his string of great seasons (1998-2003) were so great. But all the receivers Macey could compare Moss to all declined significantly after they turned 30. Moss just turned 30 this February.
There is just too much risk in trading for Moss. Not only could he be a disaster off the field, he might not be good anymore on it either.