There's really no need to add such a badge. Every badge exists for a reason. These weren't just dreamed up based on someone's whim or because someone felt there needed to be some sort of dress-right-dress symmetry or rule where there must be 3 of something per category just because there are 3 classes of badges.
In this case, a bronze badge would accomplish nothing except waste some developer's time, who should instead be focusing on fixing bugs or tweaking the review system. However, 30 days says a lot about the health of the community and the dedication of the user. 30 days is easy to get, you are right about that, but it also means users with that badge have more than likely participated on the site in some manner.
Even if you're just refreshing the page and clicking on a question once per day, chances are you'll see something that interests you, and you'll post an answer, write a question, upvote a post, or leave a helpful comment. In short, most people with the silver Enthusiast badge have also done other things on the site. You may not be married to the site, but at one point in time, you were dedicated enough to visit for an entire month.
On the other hand, the gold Fanatic badge takes a tremendous amount of effort to achieve. Sure, the same techniques one might use to get the Enthusiast badge apply, but because we're now measuring 3 months and give or take a week, there are just so many more opportunities for someone to make a mistake, such as forgetting about UTC, or taking a day off. In fact, many people don't get this badge on their first run. On day 73 on Stack Overflow, the clock reset, and I had to start over. Still, while I was visiting everyday, I wrote lots of answers, upvoted plenty of content, and learned quite a bit just from reading other Q&As.
The point is, people who go on badge runs for these two badges are more likely to make positive contributions. A bronze badge won't even make a dent in the site in terms of helping it out. Badges are designed to encourage users to do things that are beneficial to the site in some manner. Hope this makes sense! Good luck! :)
NOTE: I see you're an Unsung Hero holder! Congrats on earning that one. For that badge, you likely answered a lot of questions that weren't getting a lot of views, so your contributions likely really helped out! Same rules apply. That badge was created for a very specific reason. :)