I'd do the Di2 upgrade but I'm balking at the $2K price for a wheel set. Of course I'm not a competitive rider but I DO absolutely LOVE the accuracy that the Ultegra Di2 group on the Giant TCR I just purchased second hand has over the manual shifting 105 group with a triple up front that's on the 2004 Fuji Roubaix it replaced.
Your money, your choices...