To automate this process, I whipped up this quick and dirty AutoHotkey script:

^!r::
Loop 600 {
Send s
Sleep 10
Send j
Sleep 10
}

As you may have worked out, this simply simulates a press of the ‘s’ key, waits ten milliseconds, simulates the ‘j’ key, waits again, then repeats the process 600 times.

The first line of the file means “do the below when the user presses Ctrl+Alt+R”.

So all I had to do was save the script, double-click the .AHK file to activate it, then click on “Starred items” with Reader, click to open the first one and press Ctrl+Alt+R to instruct the script to start rifling through your items, unstarring them one by one. Because I had slightly less than 600 starred items, I found that the script “sticks” on the last item, starring and unstarring it repeatedly until I killed the script by right-clicking the “H” icon in the taskbar and clicking Exit.

Feel free to use my script to clear down your own starred items. If you find that the script seems to miss the odd item, you may need to increase the 10 ms delay.