Gang,
As far as I can tell, until 1960 or 1961, Blue-Point was Snap-on's wrench line. From 1962 on, the wrenches were branded Snap-on and took on the smooth, full polish, modern look that we now know.
When this change over occurred, Par-X and Blue-point became the value lines of tools; at some point (early 1980's?) the Par-X line was dropped and Blue-point continued as THE value line of tools.
That's my story and I'm sticking to it. Of course, I could be wrong; are there other theories?