Here are six other criteria from a previous thread that may be of interest here, to pick and choose from:
(1) All video content was released in Japan before 1995; The author's opinion was that 1995 puts the entire category before the "Evangelion revitalization of anime" which is arguably the beginning of contemporary anime, "... and if you watch something from '94 and then something from '96 (or Evangelion) the quality jump is almost always obvious."
My comment: a 1995 cutoff will be 15 years old by Kumoricon 2010. Not bad, seems reasonable.
Also note that Sailor Moon 'counts' as 1992.
(2) The entire video is in black and white or sepia, things like scratches and hairs are a good addition; this one has been directly carried over as I think it's fairly flawless for the category.
(3) All of the source material was originally black and white; allowing for I Love Lucy style "colorization" of old anime, which I think remains in the spirit of #2.
(4) The music one... [the author was] unsure how to deal with this one; "there's a lot of new music that sounds/feels Retro. It's practically a genre at this point." The author suggested that audio and video have the same cutoff year as criteria, but the entry only has to satisfy ONE.
(5) Define the whole category as: "Silent-style film using Classical music."
My comment: This would probably drive toward using instrumental music as well, because vocals seen like they would distract from the text-card effects common to silent movies.
(6) Using the concept "Retro" in a creative visual way, such as the use of projectors, film tape, etc; In this way Nostromo's "Running Man" fits the category and honestly [the author] felt it was more "Retro" than a lot of the Retro submissions (such as the Trigun one.)
My comment: Please remind me - which Trigun AMV? I checked the final playlist and didn't see any in 'Retro.' Feel free to post a link.
Another fact-oid, whether 'here nor there' or not: Personally I have a visceral reaction to eye designs and hairstyles as indicative of 'old school' or not. I also have a particular fondness for 5-sided and 6-sided designs of the late 1990s, and some of the earlier to mid 2000s follow-ons which added certain arched elements. Maybe it's that 'anime you first got into' effect...