Aggregate posts from subdomains on main page

I’ve been using the MU Sitewide Tags plugin for years to aggregate content on the main page from my subdomains. It makes duplicates of the subdomain posts on the main blog. I display excerpts of those posts with an excerpting widget. I have a Genesis/Studiopress theme. I also set the main page to be hidden from search engines since it didn’t generate original content. However, now some of my content originates on the main blog. Therefore hiding it from search engine bots is not good. On the other hand, having duplicate content visible to the search engine bots is also a problem.

So basically, my question is:
Is there another automated way of aggregating posts from the sub-blogs and displaying linked excerpts of those posts on the main blog? In other words, a way that doesn't create duplicate posts on the main blog?