Update for 2020:
Current tally for buying the cash close/selling the cash open: + 22,75 points.
That's not a huge return, is it?
If, however, you bought the cash open the 4th of January, 3758,50, you would be up 3832,75 - 3758,50 = + 74,25 points on Friday's Close.
So, it seems like buy and...