WoW:API StatusBar GetMinMaxValues
This appears to return only the minimum value at this time (int ver 4216). At the very least, it only returns one number.
In terms of the main casting status bar, a better way to access these values is:
minimum = getglobal("CastingBarFrame").startTime;
maximum = getglobal("CastingBarFrame").maxValue;
-Moof