The debate about subdomains vs. subdirectories has been going on for a long time. You have to be careful about reading old stuff, because the best answer has changed over time based on changes to search algorithms.
I.E. There was a time when "link-juice" was treated separately on each sub-domain, so subdomains could dilute your effort. There was also an era, when Google would allow a max of two results per sub-domain on a SERP, and so people would use multiple sub-domains to get the potential for more links on a SERP.
At the moment, they appear to be roughly equivalent And so the decision usually comes down to other convenience issues rather than SEO benefit In your case, since you're already on a sub-domain I probably wouldn't bother to move them and do all the re-directs, ect...
I'm basing this advice, largely on Matt Cutts video answer here: