Catalog is a mess with date structure, best way to proceeed?

Re-importing all of your images is the LAST thing that I would consider. If folder dates are in a consistent format, i.e. 2014-01-14 they will sort naturally into date order. If those folder date names are in different formats, change those first. (right click-rename). If there are subfolders within those date folders that don't belong there, move them to the correct folder by dragging and dropping. I don't have a clear picture of what the problem is from your description of "dizzying array of folder dates", so can't give any suggestions beyond the basics of renaming and moving, all of which must be done within LRC. Don't attempt to doing any reorganization of folders outside of LRC or you'll compound the mess.

I suspect the main reason @GoldingD is suggesting not to reimport is losing all your settings. 

You could mitigate that by going to All Photographs in the Catalog panel and then Select All. Use Command + S to save metadata to the files. 

If you wanted to then create a new catalog, you could import and have your setting intact. Make sure to set up the Destination folder the way you want the folders to appear. 

What are the issues? You lose Collections, Flags and Virtual copies. You wouldn't import 80,000 images in one go, you'd need to do it in stages, so that is time consuming. 

The other option is to do as @GoldingD suggests and create a folder system manually and move the files within Lightroom. There's no option that isn't time consuming, but this method keeps everything intact with little chance of image or information loss. 

One of the major strengths of a catalog is that you don't have to search by folder name. If you had set up keywords or other metadata to help you find your photos, you could use that.

Even if you absolutely must search by capture date, the Lightroom Classic Filter Bar will do that for you, even if the folder names are not consistent. So find photos by the Filter Bar capture date, and if necessary, move them to a folder with a better name.

Or, if the issue is not finding the photos, just getting a consistent folder name, use LrC to rename folders manually so that the naming is more to your liking.

But really, there are much better ways, keywords and other metadata. I never search by capture date to find my photos. Better you should spend time keywording than fixing folder names, you will accrue many more benefits than simply fixing folders.

So, do not re-import. This is so important, I am going to say it again. Do not re-import. And @GoldingD has also told you that as well.

DO NOT Re-IMPORT.

Consider, in LrC, creating a sensible file structure within the Folders Panel. In other words, restructure the folders. Something you like, something that makes sense to you. Then withing LrC, using the Folders Panel, move them images into the desired folders. This will take time.

some links:

• https://helpx.adobe.com/lightroom-classic/help/create-folders.html
• How do I reorganize my Folders panel? | Lightroomk Queen
• Lightroom Video Tutorial: Organize and Manage Your Photos and Folders | Laura Shoe
•  

In theory, you could do this outside of LrC, but then you would have to accomplish a lot of corrections in LrC in the Folder Panel. Some may try that as the Folders Panel is not a Folder Manager, and they would prefer to use the OS folder manager. But you would wind up with lots of folder issues, lots of missing photos, that would then need correction, as in:

https://www.computer-darkroom.com/lr2_find_folder/find-folder.htm