I don't know if they still do it now, but when they were Hacker Safe they actually did a pretty extensive crawl looking for security holes daily. I always thought it was bullshit too until I started looking at the reports they generated.
Re conversion rates - again, not sure if they still do this...but they used to do a 30 day A/B test (with and without the logo) to see the conversion rate difference and gave the option to get your money back if you weren't happy. In my case, the lift more than paid for the expense. I think I saw a .5-1% difference, it was awhile ago so I don't remember the specifics. Annualized, that came out to over 200K in sales - way more than the expense of the cert.
This is all old info though, not sure how it is now.