With all due respect to larryselbows, I've seen grad school as being easier.
As undergrads, we all have to slog through classes that, for the most part, are either (A) not really related to our major of choice (i.e., history majors being forced to endure biology classes) or (B) just plain aren't interesting to us at all.
As a grad student - in terms of classes you take - you are now specializing yourself to a level where you only take classes that relate to your choice of study (and, by extension, what interests you). I'm doing physical chemistry grad work, so I only take physical chemistry classes. So in terms of academics, grad school is fun. Sure it can be difficult; even if you like the subject/class, there will undoubtedly be something that makes you scratch your head, but herein lies how well you rise to challenges. When I confront a physical chemistry problem that stumps me, it just fuels my fire to figure it out. To me, that's fun. But I also understand that not everyone will think thusly.
Aside from academics are the - for lack of a better term - "administrative" things. Grad work, at least at the Ph.D. level, requires you to suffer through 1st year written exams, 2nd year seminar presentation(s), 3rd year oral exams, and finally a 4th year dissertation defense. While those can induce stress, again I think the "problem" distills down to how you rise to the challenge. I just finished my 2nd year exams, and though I was surely frightened, I found the challenge almost fun. If you find yourself easily motivated to go out there and hit home runs, then grad school is for you.
Regarding the concept that grad school is for the smart(er) people: I don't buy that. I have been told - and am witnessing in others around me - that "triumphing" over grad school is as much a test of perseverance as it is intelligence. If you can ram through 4 years (or 2ish for a Master's) and not find it sapping your perseverance center of your brain, then you will come out just fine.
Practically, getting a grad degree will net you - on average - a higher salary down the road. Sure, you've effectively forfeited a few years of B.S/B.A.-level salary to get the grad degree, but it will be made up with your higher M.S./Ph.D. salary. So there's a payout there surely.
Don't concern yourself with being "overqualified." In today's world, grad degrees are becoming the norm. A B.S. in a science nowadays will net you a job as a lab tech. An M.S. too, but just higher up on the totem pole. A Ph.D. gives you so much more - the power to create your own research projects, manage people, and be at the forefront of research. At least it is within my world of chemistry.
Go for it.