Photos will not download Photo Stream photos

I know this because I also have iPhoto set up to download Photo Stream photos and I am seeing photos in there that aren't in Photos.

That is probably the problem.

Only one photo library library on your Mac can sync with My Photo Stream. If you enable My Photo Stream for an iPhoto Library it will stop syncing to the Photos Library.

I still get the same request to upgrade my storage on iCloud. And nothing has downloaded from my Photo Stream to Photos.

This is incredible.

The iCloud storage has nothing to do with My Photo Stream. My Photo Stream does not count against your iCloud Storage.

You should only get the warning to upgrade the iCloud Storage if you are using iCloud Photo Library, but not for My Photo Stream.

Your screenshots are only showing the System Preferences. What are the settings in Photos > Preferences > iCloud?

Is iCloud Photo Library in Photos > Preferences > iCloud enabled?

Perhaps the preferences files are corrupted and your settings in Photos do not take.

Try the following:

Quit Photos, if it is running and then delete the following folders from your user library, the complete folders, not just the contents.

~/Library/Containers/com.apple.Photos/

~/Library/Containers/com.apple.photostream-agent/

~/Library/Preferences/com.apple.Photos.plist

Your user library may still be hidden.To reveal the hidden User Library:

• Bring the Finder forward by clicking on the Desktop or the Finder icon in the Dock.
• Select your user/home folder (with the house icon in the Finder sidebar)
• With that Finder window as the front window, press the key combination ⌘J to bring up the View options.
• In the View options panel enable ’Show Library Folder’. That will make your user library folder visible in your Home folder.
• Open your Home folder, then the Library folder, then Containers.
• Move the complete folder ~/Library/Containers/com.apple.Photos/ to your desktop. Move the entire folder, not just the contents.
• Remove ~/Library/Preferences/com.apple.Photos.plist as well.

Sorry, I forgot to mention, that you need to restart the Mac after trashing these files.

Try again, but this time restart.

(though never found ~/Library/Preferences/com.apple.Photos.plist).

Can it be, that you looked in the Library folder rat the top-level of your system drive and not the hidden Library folder in your Home folder?

If ~/Library/Preferences/com.apple.Photos.plist is not there, it might be an indication, that you are having problem with file ownership and permissions on your Home folder. Then the preferences you are setting might not be written to the preferences files.

See Linc Davis's post how to reset the home folder permissions and access control lists.

https://discussions.apple.com/thread/6587728?answerId=26800021022#26800021022

You might ask for help with this problem in the El Capitan forum.