1. Yes, absolutely. I love learning. I dislike that courses are only 8 weeks long because I would like to dig deeper into the material than that timeframe allows. However, I definitely feel the time is well spent.
2. I am less concerned about the credential. I already have a bachelor's degree and some graduate school. Thus, it's not likely to give me any extra weight, and I don't plan to pursue jobs with it. However, some of my colleague who've moved on have found it both helpful and valuable in that regard.
I will note that the school is nationally accredited, so this can be quite limiting (e.g., grad school options are very limit, transferring credit is limited, etc.). So, this is a consideration that must be taken. However, I'm happy with the return on my investment (knowledge) so far.
3. Real, college credit which can be transferred. While it has limits in that regard, I am not aware of any colleges that will accept MOOCs for transfer unless they were explicitly designed to be credit granted (e.g., some of edX's stuff or maybe some Coursera's new stuff).
That said, I would argue that UoPeople is really "self-teaching" like you would with MOOCs. While the school implements a form of "peer learning," I find it to be poorly done and not very helpful. I do meet some others who are genuinely interested in the topics, but most students are just interested in getting through the courses.
And, ugh, I loathe peer assessment. While it's not the only form of assessment which takes place, it's the most obnoxious part of the school. It's worse when you peers don't understand basic things like how files and directories work.
This part term I was told by a peer, in the discussion forum, that my post was "wrong." (It wasn't.) And the student told me to read so-and-so's post to see why. The student subsequently marked me down. (Fortunately, it had minimal impact. So I didn't bother appealing it.)
I couldn't really give any advice for your son. If he can handle academic work on his own fairly well, then it might work for him. However, some students struggle with online learning and there's not a lot of support structures in place at the school yet.