Ultimately, getting an EA is going to be worthwhile. It will open a lot more doors for you, and won't require going back to school or anything like that. But it's still "book learning," which needs actual experience to back it up.
It will probably allow you to find some kind of seasonal work at an actual firm, where someone with more experience reviews your work and you learn the forms. If your end goal is to be self-employed, then you want to be confident in your abilities so that you avoid liability issues from being incompetent. Sometimes I think people become EA's and think "Great! I can prepare taxes now! Clients, here I come!" You should put a couple of busy seasons between your certification and going solo, so that you've worked out the kinks in your basic knowledge.
I've heard that places like H&R Block are more about selling than doing a good job. It's probably not the best place to prepare you for running your own show.