This is a bit related to the question: Are "has this been studied before" questions on topic?
If I post something in the arxiv, can I ask for an opinion as to whether: 1) it's been done before 2) it's worthy of publication 3) and if it ask for recommendation of appropriate journal.
Due to the highly subjective nature of the answers not sure it is allowed. But mathoverflow would kind of be the ideal place for this. Not only is this an organized professional community. But many folks that are not currently in a math department or not even professional mathematicians find it difficult to find this type of information.