Badges are something to be worked at and are a sign that you are contributing to the site. There are a few easy badges to get you going such as the "Student" and "Teacher" badges but the majority of them require at least some work and having more "low level" badges would seriously dilute their value. There really are quite a few badges out there, there are even tag badges which require a reasonable amount of work.
There is already the "Enlightened" badge - "Visited the site each day for 30 consecutive days" so why would another similar one make things better?
There is even the "Electorate" badge which encourages exactly the behaviour you are looking for: "Voted on 600 questions and 25% or more of total votes are on questions" and is a gold badge, how could that not be incentive?
To me the badge system is a thing of personal pride, not like the achievements you get in games where you "win" an achievement simply for mundane things like "ran the game for the first time" and "killed your first bad guy" and other "achievements" that aren't really because you're simply playing the game.
I personally have 34 badges on SU and only 9 of those are silver, only 1 of those 9 is a tag badge. Each one of those badges is a mark of putting in some level of effort in the community so if you carry on helping out you'll pick up more badges as a simple matter of course.
While badges show your involvement, they shouldn't be your only reason for being on the site.