Same problem I have. You would think there is a way to download more apps on a Vizio smart TV from the "Yahoo Connected TV Store" App? All I see in this app is information about my Yahoo account, profile, etc. I cannot find a way to browse and download additional apps.
If after trying the options described above, you are still having problems with the app, you may need to perform a factory reset for your TV. Refer to your TV’s manual for instructions on how to perform a factory reset.
WARNING: You will lose TV settings when performing a factory reset, including the personalization of your apps – the list of apps you have, their signed-in state, and any other customizations.