I agree 100% with Aida's statement "These "classic" items still change, even if just in small ways, over time and they most often do need to be updated to keep looking current".
And even trendy items - I see it often said now that you can thrift trends (like the current platform and wideleg trend for instance, by finding them secondhand from an earlier cycle of the trend). I disagree SOOO strongly. Even though trends come around again, there are differences in details or even just fabrications. You will not truly look on-trend wearing these. Keeping things for when they "come back into fashion" fails for this reason.
OTOH that doesn't mean I wouldn't wear a 70s shoe, or a pant circa 2000. I would; just not with the goal (or illusion) of being "fashionable". Like, if you're wearing the classic item that happens to be from 1985, know that it is from 1985 and don't pretend to yourself that it's anything else. Go into what you're wearing with consciousness. As long as your goals are clear and you understand the parameters and effects, and it still pleases you, you can wear anything.