At this point I have no idea why the DI Update didn't work, but the speaking functionality is not on your Pi. Do you have a Dexter_Software_Update_log on your desktop? Would you mind uploading it here for me to take a look?
While I look into the DI Update issue, let's look at getting your GoPiGo to speak.
Open a terminal window
enter the following:
sudo cp gopigospeak ~/Dexter/GoPiGo/Software/Scratch/GoPiGoScratch.py
If all goes well, doing a grep afterwards will give a different result
grep SPEAK /home/pi/Desktop/GoPiGo/Software/Scratch/*
And I apologize for taking so long before coming back to you..