Reposting an old blog, IMHO, is simply a bad idea - period. In academics, it is considered self-plagiarism if you use the body of your previously written pieces without citation. I've got a bunch of quality posts that didn't make a penny when I first started writing here. Sure, I've been tempted to repost, but never have because it is, as you've mentioned, "double dipping".
I have taken a few of my off-site content and published on Steemit - but I have also clearly stated that it was reposted and the link to the original article.
If you do a Google search, you will see that Steemit articles are being listed. The bots recognize key words, headers, photo ALT text, and backlinks. These things help a writer because Google search will (eventually) recognize you as an authority on the subject and bump you higher in the search engine.
That being said, to simply copy and paste, even if it's off-platform can have a detrimental effect.
My suggestion is to write a new post and backlink to the archived ones using appropriate tags.
And @anyx, speaking of tags - maybe if the people running contests and series posts used a specific tag - something that the general public wouldn't have a reason to use regularly... like "sequence", cheetah could then ignore that post. I would recommend spot checking to make sure it's on the up and up, but certainly not every single time. :)