WebWasher may have an effect if web shield is monitoring content and then WebWasher is filtering ads. You would need to ensure that the two proxies are working together and it would be better if ad content was removed before web shield monitors. That may well not be possible.
My Firewall can filter ad content, as can my browser firefox, all without having to use a proxy, so I don't need another ad blocker or the extra complexability.
Web Shield in my opinion is absolutly essential, Standard Shield is trying to catch something that is already on your HDD (which may be more difficult to remove), Web Shield can block before it gets on your HDD. No contest, protection in depth.