The predominant answer around here seems to be that it's not worth it if you are doing it for external rewards because the experience you could gain in that tim

The predominant answer around here seems to be that it's not worth it if you are doing it for external rewards because the experience you could gain in that time would be better. More work experience might be a better way to improve your skills. However, if you're doing it for personal reasons it might be more justifiable. I did undergrad in EE/CPE in the US and I always felt like, personally, I need a "real" CS degree, which may be a bad reason. I guess you need to decide if the Mech degree is actually hurting you somehow? But also I went for a masters degree because I wanted exposure to CS fundamentals, which I think is a good reason: compilers, operating systems, artificial intelligence, data mining, etc. Depending on the job, you aren't likely to pick those things up on your own.