I've changed my password and security questions several times and had several phone conversations with PayPal fraud security people. While it is not clear what the scammers are trying to accomplish, it is somewhat annoying. I actually think that Sid is on the right track.
Unfortunately, it is relatively easy to get one's PayPal email address simply by making a small purchase and then not paying. It is then quite easy to send a small payment to it and see if it is a valid email address attached to a PayPal account and if the account owner is actually monitoring activity on his or her account.
Unfortunately, even changing the email address attached to one's email account only seems to slow them down until they obtain the new one. I must admit that whoever the scammers are they are persistent.