Is there a way I can perform a search in GMail which will return all emails where I have been listed as one of many email addresses in either the To: or CC: fields?
Basically emails where I am not the sole person being emailed.
Your best bet is probably to download them via IMAP and use a mail client's more powerful search capabilities if you value your time.
If you're intent on using the browser, in Gmail settings, turn on personal level indicators and set your maximum page size to 100 conversations/page. Then do a search for 'cc:me OR to:me'. Then do a find in page for the character › (which will highlight messages that are sent to you+others. This might take a while, but is way quicker than sorting through them all.
The Gmail search field let's you put to: and cc: operators. However I'm not sure how you could get only those ssn to you but where there are other recipients. Maybe try to see if you can add boolean operators (to:youraddres AND cc:*).
How comfortable are you at coding? We have an email API which would let you code that sort of things: http://context.io. If you look at it and have questions, let me know: firstname.lastname@example.org