In my experience, an email address copied from the From header via a right-click > copy address will paste without a mailto prefix in Numbers, or anywhere else. If you are copying an email address hyperlink from the email body text or a signature, the right-click option becomes copy link, not copy address, and in that case, the link is denoted by the valid mailto: prefix.
I do not use Wufoo forms or Google spreadsheets.
A quick conversion of that mailto: address to an ordinary Mail address would be to option + left-click that linked email address. This will open a new Mail compose window with the converted email address in the To: header field, and that you can then copy/paste into your Wufoo forms or spreadsheets. Then click the compose red traffic light to dismiss it.