I would only like this "feature" if I explicitly opt-in by clicking an "email me if this product goes on sale" button. Starring / adding to favourites etc. is not consent to send me an out of the blue notification. For all they know I've already bought the game somewhere else, or my interests have changed, or I don't play games anymore.
I'm tired of technology trying to guess what I want. When they get it right it's creepy. When they get it wrong it's annoying. I also really hate "out of the blue" emails or notifications. My "aspergery" personality has a hard enough time dealing with texts from my family members.
I'm in the habit of turning off all notifications off for everything. It just bothers me how often the defaults are "everything on."