If I'm understanding your question you are looking to get a total count of layers represented in the legend? If so then you could use:
mxd = arcpy.mapping.MapDocument("Current") df = mxd.activeDataFrame legendCount = len(arcpy.mapping.ListLayoutElements(mxd, "LEGEND_ELEMENT", "Legend")[0].items)
I want to know how many columns in the legend element. Not how many items in the legend.
I hope It is clear now.
Can you explain why incrementing adjustColumnCount doesn't work? It seems like you should be able to:
1.) make any changes to your legend
2.) record the current (original) legend elementWidth
3.) increment the number of columns using adjustColumnCount
4.) when the incremented legend elementWidth = the original legend elementWidth, you know the number of columns
The default for column count is 1 if your trying to increment a legend simply start or reset the legend to 1