A crap Linux cert will be crap. There are some good ones though, like RHCE. You can be Linux admin for years and still not pass without heavy studying. That's because there's a lab component to it.
Is it worth it? Maybe, if you're trying to sell your services, either in the form of a HR bypass filter ("Look, he's certified in Linux!") or as a consultant ("You should trust our team because we're all certified"). I know only 2 people with certs, and they fall into the latter category.
Most of the time though, I think it's not going to be worth it. If your current work will pay for it and you're willing to put in the work I can't see any negative aspects to having it, but I don't necessarily see the return on investment.
