For artworks, nostalgia may not be a factor, but being original and considered "classic does" does. If you painted a picture similar to "starry night" or "mona lisa" with better technique, you're probably not going to get famous because people already have those original painting ingrained in their minds (ie. replicas are not nearly worth the same as the originals). In addition, the mona lisa is no longer famous just because it's a good painting, but because it's become a large part of culture and there are too many references to it. At that point, it may no longer be about the quality of the product, but rather the name of the brand.
The 80s series were considered "classic" because they were the first to make it big (the 70s ones are not nearly as famous).
And as tape already mentioned about standing the test of time. You have to admit that a major entertainment factor in wuxia series IS the "wuxia" part, which will inevitably involve technology which no doubt will change with time. The quality of the series isn't only judged by the screenplay and acting/directing, but will also be judged on cimetography, costume design, set design, choreography/sfx, etc (which is dependent on technology/funding). Except for hardcore wuxia fanatics, I don't think most of the generations born post 2000s will want to sit for 40 hrs to watch a series from the 80s.