Well I assume some of the female cast members have had ear piercings over the years, hehe.
Well, ear piercing isn't really that big a deal, since, well, it's been pretty common for women to wear some frm of jewelry on their ears, whether they're earrings, piercings, what have you...
I mean, I can see why someone with a nose ring, or nose piercing, whatever, would seem a little unexpected to people, especially on a kid show, but there's one thing that SST, and the Muppets in general, have been known for, and that's keeping up with the times, and it's really relevant: look at the 70s how many sketches and inserts reflected the disco era, or the 80s when everything was all neon and "glam" and everything... in our modern-day society, it isn't uncommon to see someone with some form of body piercing, remember in MFS, Sam's jaw dropped when he saw a teenaged girl dancing, exposing her belly, which had a piercing in the belly-button... or heck, The Dot in IAVMMCM was a BIG example, I found that a lot more disturbing than someone on SST being seen with a nose ring (plus, heralde has a point, Leela's nose ring could have cultural significance). Or even more recently, Miss Poogy and her borderline S&M getup.
Is it inappropriate to expose kids to this? Well, I think that is mostly up to how parents feel about it... a nose ring may or may not sit easily with some parents, but suppose she had other piercings? Like say, her brow? Lip? Even tongue? That may be pushing a little, but who knows? I think mainly it's those who are more old school as far as their views go are more likely to think such a thing would be a little inappropriate... it's sort of like myself and The Squirrely Squirrels: I wanted them to reflect today's mainstream contemporary fashion, with their clothes and colored hair, they project a desired image, but isn't too overtop... now, had I gone a step further with piercings, fishnets, little leather straps and chains, etc, that may have been pushing it a little.
What's funny is that reading in the 40 Years book, Emilio Delgado said they had asked him to shave off his mustache when he had gotten the job of being a part of the cast... I wonder why that was? Gordon had a mustache, why couldn't Luis have one too? What Luis have been like with a mustache?