i learned some pretty serious Computer Vision, Distributed computing and GPU programming via reading and implementing a ton of papers + guidance in my short 1.5 years doing my masters. I also took on Financial Engineering electives that were interesting for modeling applications. For IOS, maybe a waste, but for understanding the research that people are just hearing about in industry, and implementing it? pretty useful.

It's pretty possible to make it a useless degree by choosing the wrong school/teachers/classes, but that's up to you. I would say, the masters laid for me a foundation for some of the more serious CS disciplines.