I can only speak for myself. If I cant act on a report, I usually leave it in the queue. For example, if it's for plagiarism, but involves a higher ranked account that I can't nuke, but it was reported within a section I moderate, I usually leave them in anticipation that a staff with the appropriate permissions looks into it further. While, this example is a little different to what we have here, I would expect that a similar process might happen.

I can't for definite tell you the best way, personally I think indvidual reports can be good at times, especially when a thread isn't covered from top to bottom in spam, however when most of the thread is spam, or it's overwhelmingly congested with spam, I think reporting the original thread could be best, indicating that there's several posts that need to be removed or maybe not the original thread itself, but a spam comment in that thread. Users do this for bumps, instead of reporting every bump individually, they report the most recent one that needs to be removed, and indicate that several others have been made. I think a workflow similar to that might be beneficial, otherwise the moderator reviewing the report might think your expecting action to be taken on the original thread itself, which wouldn't be the case. 

Personally, for me I don't see too many problems with the suggestion, although I'd willing to listen to anyone who has any ideas on the best workflow. I think the amount of reports we've recieved the last few months is rather unprecedented, and isn't something that usually happens, and since this thread has mostly been exhausted, I don't think we'll be seeing it too often in the future either. So, the issues really only start to seep in when we have exceptional cases like this, otherwise reporting as you normally would is probably fine.

Not sure if that makes sense to you guys at all. However, I think when there's a thread covered in spam, and I mean top to bottom, and it would result in hundreds of reports, I think potentially reporting just a few, and indicating there's more could be the best idea to prevent spamming other moderators report queues, that might want to be dealing with more urgent matters.

This is kind of the reason I'd like to see the report page with the ability to filter, so that things like this would not affect those that don't want to see it. Also, would be useful for local sections.