A girlfriend of mine got her nipples pierced vertically. It was *damn* hot, and they were oh so very much fun to lick, pull and flick once they healed up, which took about 2 months until she let me play with them again. She'd get me to clean them too, which was a lot of fun. According to her, it didn't make them more sensitive, but it did make her much more aware of their existence, and, being a slut for pain, constantly horny for about 6 months after the fact 😄
Some years later she had major surgery and had to take them out, and the piercings healed up enough in the 2 hours they were out to not go back in. Damn shame too, we had slave rings (normal bar, with a hoop attached to one end) on order 😢
She has small nipples, so the scar tissue made her apprehensive about piercing them again.
Knowing that, if I had even *slightly* better luck with piercings I would absolutely get mine done.
One thing I didn't like is that after she got them I could never squeeze her nipples as hard as I wanted to/used to, it would hurt just as much with less than half the pressure.