Here's a bit more troubleshooting info. Starting version: 2.10, build 670. Deleted the Sencha Architect 2.0 folder in my AppData\Local folder. Start up Architect, say no to the 676 update, log in with my ID, etc. Open exisiting project. Toolbox is nice and full. Create and save new project (without adding any components), close and restart Architect, Toolbox still good. Add some components to new project, repeat, Toolbox still OK.
So in my expert opinion, I have no idea what was causing the issue. Actually, that's not an opinion -- it's a fact!
Copy that directory and then remove all of the .ion files
This should bring down the size to something you can attach.
Good point, Phil -- Aaron PM'd me, I think we are focusing on the localstorage file at this point, right? Which is interesting because even though he said he didn't find the one I uploaded to be corrupt, I did try just deleting that and restarting Architect, which restores the toolbox....