I was careful with mind-reading minor NPCs during the expansion - the worst parts was when I did mind-read a few people only to get them thinking about something really stupid such as what color socks they should be wearing or what would happen if a fox and a cat joined together. EXP just flew out of the window for such things.
Mind-reading NPCs who are important to a plot seems to pay off more though and mind-reading important NPCs also pays off.
You could always save just before mind reading someone
