As a costume designer and an Egon fre@k, it's interesting to me that Egon Spengler's clothes are 1940s, not 1980s. Younger viewers who didn't live through the 80s might not catch that his look is about 40 years older, because all the clothes are vintage and "old" to their eye.
It implies a lot about Spengler's backstory. They could be his Dad's suits and ties. All of the suits are very high quality. The sweater vests and overcoats, too. Perhaps his family once had money and lost it. Perhaps his father died young and Egon wears his suits to be close to him. Perhaps he idolizes the scientists of the 1940s like Dr. Alfred Kinsey. Perhaps Egon was a poor scholarship kid who got into the Ivy League on merit, and can't afford modern suits. Maybe it's how his mom dressed him in his childhood and he still dresses like that because, rules.
It emphasizes his Autism. We often dress for reasons other than fashion and trends. We look like people "born in the wrong time". We wear safe clothes, or "uniforms".
BTW: Ray's costume holds notes of the 1950s and he's still wearing the same flannels and black T-shirt 40 years later. Way to represent Autistic culture, Dan💛. I would kill for Ray's green wool coat and wide leg khaki's in GB1984.
