This isn’t to prevent spam, it is to identify the original leak. If the unique email address you gave to company X is used for solicitations by company Y, company X must have given it away.
Depending on my mood and whether the company is local, write a complaint to the company that leaked the address or to an appropriate government institution. In my country, a local computer security news site started a tradition of telling the offending companies that they can either apologize and donate some money to a charity (and send back the proof of payment), or you'll bring the issue up with Personal Data Protection Office, which will be more than happy to fine them.
Most spammers won't go through the of "gaming" it. There's no upside. There are far easier targets to focus on than sending more mail to a single recipient who is more sophisticated.
