So, I closed Safari, went to ~/Library/Preferences/ and found com.apple.Safari.plist and dragged the file to the trash. Then, I relaunched Safari and re-enabled all the prefs that I like, like View—>Show Status Bar, and then went into Safari—>Preferences—>RSS and clicked the Remove Now button again. Ta-da! Safari RSS works again! Thanks, Scott!
Shortly after getting Safari RSS to work again, I realized that my Debug menu was missing, so I closed Safari, launched the Terminal and typed:
defaults write com.apple.Safari IncludeDebugMenu 1
Hit return. Then relaunched Safari. There's the Debug menu. All is well, again.
I'm not looking forward to this becoming a regular thing. I hope Apple fixes whatever buggy bit is causing this.