Goggles make sense in a steam powered environment too. If every contraption that surrounds you is powered by coal and steam, the air will be rich and sooty. Goggles are also important when tooling around at high altitude in ones semi-rigid airship or Orinthopter.
From a costuming perspective goggles are a perfect accessory. They set the tone for the whole costume, and they fit everyone.
When I started making my steampunk costume, I found these great old safety glasses on eBay. They had a nice brass coloured patina, so I didn't have to do any repainting. I think they date from about the 1930's but I could be wrong. To kick them up to steampunk standards I added a set of jewellers magnifying loupes to the side with some gold coloured wire. I think they look smashing, and I have worn them both with steampunk outfits and with my Harry Potter Ravenclaw wizard costume.