I've been thinking about this question since seeing Logan's Run (again) recently.
First, perhaps we should define and agree on what we mean by "dated". Just because you can tell when a movie was made doesn't necessarily get it labelled as dated. Sure, you can probably tell Alien was made around 1979 based on the technical look of the film (film stock, color, lack of digital effects), but that's generally what we mean when we say something looks dated.
Usually, I think we are talking about hair, clothes, or interior design that was very much contemporary with the production of the film.
Which sci-films look dated? Which don't? Does it even matter?