I think it's better to disallow original research (specifically, original-to-LW research), or summaries of external content which is not LW-canon, without clearing it by the community by posting first. After that, if the post gets an OK reception, a moderately detailed summary referring to the same sources as the blog post can be made on the wiki.

Richard Kennaway made a good summary:

the workflow should [be], independently of each other, both "idea for posting --> write post" and "notice something generally accepted on LW without a wiki page --> write wiki page".

This is also not a new idea. From LW wiki user guide:

Since the Less Wrong Wiki is intended to summarize concepts and link to longer discussions, please think carefully before making the summaries longer - this may just cause users to get lost. Ask whether your further details, extra clauses, or added links, are of equal quality, relevance, and importance with the existing material