I am not going to comment on the bigger picture of whether amateur astronomy questions are good for the site, but I can comment a little on the second part.
An SE site about astronomy can provide value, even with other sites, because it isn't a forum.
I gave a talk a few weeks ago about the site I help moderate. One of the things I brought up several times, is that forums facilitate discussion, but SE facilitates getting answers for real world questions.
I ran into this last night while looking up something. I can't recall the exact topic I was researching, but it was essentially about one of the various special purpose filters. I found several threads on the forums about the filter. Each thread led off with a question about the filter. Then there were many posts the followed
- some asked where to get the filter, and what the best price was
- some were just "me too" posts
- some where "I have it but I haven't tried it yet"
All three of these types of posts would have been deleted here, leaving just the answer to the question.