You are correct that clitoris piercing is rare, but it is done. I know because I had mine pierced about 5 years ago. I am fortunate to have the right anatomy, with a largish clit. It was quite intense, for a moment, ached for a few days, and then gradually became a joy! ;-)

Sensitivity was greatly increased in the beginning, to the point of almost being unbearable, but now it has settled in, and for most of the time I hardly notice it. I occasionally get a surprise sensation when I sit a certain way, not painful, but just a nice tug. It is fantastic during sex, and has changed my whole orgasmic response.

It is risky however, and I would not recommend it to everybody.