At $99, it's almost a throwaway purchase; very little risk involved whether or not it pays off in entertainment value.
If there are even just a few exclusive games on it worth playing, or if there are a bunch of Android only games that cross my radar (I have an iPhone, not a Galaxy), it's worth it. It would almost be worth it for emulation alone. A really inexpensive box that uses up essentially zero power that automatically syncs with a game pad that is super portable and easy to hook up to any HDMI display; what's not to like?
I rarely use my overclocked gaming desktop PC because of the power draw and most of my computing tasks are just as easily handled on a quad MPB laptop that uses less power. For a lot of tasks that don't even require a desktop OS and apps, I won't even use a laptop and will just use a tablet.
So the whole "I'll just use my 750w desktop PC to run old games in emulation instead" is kind of pointless to me. Why would I even turn it on for something that could be handled on a $99 dongle?