Upload file directly from a URL in upload (File/Open) dialog

Once you find the file using Alfred, you can copy its path to the clipboard and paste that path into the Go to Folder tool of open/save dialogs.

Find your file in Alfred, press the right arrow key to view the list of operations for that file, the up arrow key to go to the last option (Copy path to clipboard), and then the enter key to activate that option.
Switch back to the open/save dialog, press cmd-shift-g to open the Go to Folder dialog, paste the path in, and hit enter. The file will be selected and you can hit Enter to open/save.

If you're interested in getting some more flexibility out of Open/Save dialogs, I highly recommend Default Folder X. It's immensely powerful and customizable and could eliminate the need for workarounds like this.
$35, 30 day trial

I had a similar issue. I moved the files:

com.apple.finder.plist
com.apple.sidebarlists.plist

out of

~/Library/preferences

And then "turned it off and on again", ie. restarted. This fixed the issue for me.

My hunch from looking at the crash log was that it was somehow choking on Finder itself (the logs in Console.app reported the key found to be null was "dateModified"), and that some sort of corrupt settings were to blame.