There are few points to consider.
First, I'm a big fan of uncommon and underused names. A few that I've suggested and/or given the thumbs up to include Atlas, India, Endellion, Journey, Leocadia, Hadley, Gideon and Malachi. The world does not need another Emma or Jacob, even though both names are pleasing.
But I think the desire to be unique can go too far. The following strike me as so unusual that they don't make for good choices:
* Choosing a common name and opting for an outlandish spelling to make it "unique."
Kaelyy or Peightyn isn't unusual; it's just misspelled. I think any name is half sound, half appearance. If the sound is common, then the name *is* common, no matter how many vowels are added or changed in the original. Four heads still swivel when you call "Chaela!" on the playground, and your kiddo will never, ever see her name spelled right on the first try.
* Choosing a noun name that is an awful lot to live up to.
I've given the thumbs down to Jolie as a first name more than once, because what girl wants to be named Pretty? While few people speak French in the US, jolie is one of those words that kids pick up, especially in high school when everyone's taking languages. Imagine - you're struggling with braces and acne when your classmates discover your name means pretty. Ouch! Likewise, some names are overly masculine, like Maverick. It's got an appealing sound, but it's too cool, too gunslinger for everyday use.
* Choosing a noun that has a negative meaning.
Bane sounds like a good name for a boy. Caprice sounds like a good name for a girl. But there's more there than sound. The definition for the first is, roughly, burden. And the second means fanciful - but also cruel.
* Choosing an exotic place name and changing the spelling.
Place names are fabulous. But changing Havana to Havannah is awkward. An unusual name that everyone can spell is the best of all worlds. An unusual names that everyone *thinks* they can spell, but you have to correct? Shudder.
* Inventing a name that doesn't have roots.
While I agree that most names were made up at some point, many of those creators were writers of rare talent. Shakespeare is a biggie. I don't write as well as Shakespeare, so I'm willing to concede that my DIY approach to naming might also fall short. So while Gracelyn is a pretty elaboration of an established name, Miloynia is just a random set of syllables strung together.
* Giving a name that has no escape route.
If you name your daughter Langston, her middle name ought to be clearly feminine. If you name your son Jory, his middle name ought to be something a little more common. Langston Kate and Jory Alexander are great names. But giving your kiddo the equivalent of Moon Unit - unusual first, unusual middle, no nickname options? Big mistake. Your child might grow into the name, but odds are better that your child will never be comfortable with it.
We've got not just 500 years, but all of written record to comb through to find names. I agree that there's no need to stick to the Top 50, Top 100 or even Top 1000 when choosing a baby name. But people come to Yahoo! Answers to get honest reactions from a wide swath of the community. And if an idea is less than great, you'll know - not only will the John/Ashley crowd not care for it, but neither will those of us who routinely give the thumbs up to the more exotic monikers out there.
One final point - unique means a set of one. Leocadia is a seldom heard name, taken from my trusty Book of the Saints. But even if I name my daughter Leocadia, or Leacadie, she won't be one of one. She'll be one of a handful throughout centuries. I think that's often the best we can do.