Thanks Dan. I like the thought of accessing the few tools I need in a "lighter" manner, and that might have been what Freddie was aiming for too. I'll have to give your suggestion a little more thought, but for now, I'm just trying to have something so I can move on.
This is part of the addin I'm creating from my AML/Avenue days, with some added features. I've been the only one using it in the past, but trying to make it more flexible so I can train others. Chances are the user will have the latest version, but you never know. I typically store my custom scripts and custom toolbar within the addin build structure. I could copy the Tools I need directly into the custom toolbar I guess, and grab it from that maybe? I'm not sure if that is what you are suggesting or not. But in any case, it needs to be available to the addin.
As for you other comment about it being whether arcpy.GetInstallInfo()["Version"] is backwards compatible...I'll have to test that. But I think it will work for what I need for now (10.3)...and it looks like it's been available since at least 10.1. I'm sure there would be other missing tools or issues if used with a version prioir to that....and actually I never liked the random points from a few version back....created random, then sorted them from north-to-south.....defeated the purpose for us. But that has been fixed now.
FYI - this is the final code I added to grab the toolbox for this 10.3 installation anyway.
myDir = arcpy.GetInstallInfo()["InstallDir"]
toolboxPath = arcpy.os.path.join(myDir, "ArcToolbox\Toolboxes\Spatial Analyst Tools.tbx")
arcpy.AddMessage("toolbox {}".format(toolboxPath))
arcpy.AddToolbox(toolboxPath)
In case it helps anyone else. Not the only way to do it, but it works for me.