Mailwasher has a column that indicates if an email has an attachment.
So if you want to delete all attachments just sort by that column, tick the relevant deletes and hit process mail.
Why do you need to look at the headers of every message in mail washer?
I find I only need to look at headers rarely then it's usually only on virus emails to check if I know the real originator of the mail so I can alert them to the virus.
Most of the time I just sort by the message category, if a message in the blacklisted or "probably spam" category has an address I know or a subject that may not be spam I save it from deletion and blacklisting for a closer look in the Mailwasher preview.
If you get so many virus bearing attachment you may save a lot of time by persuading your contacts to run AV software!