These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Harsher in Hindsight: Ed Wood's cameo as a drunken bum, which is pretty much what he would become in his later years.
Inferred Holocaust: Plan 9 is to stop humanity building a "solaranite bomb" and destroying the universe. Yet Plan 9 fails. What does this mean for the universe? Given that it's the Plan 9 Universe, total destruction may be merciful.
Older Than They Think: Criswell's opening line — "We are all interested in the future for that is where you and I are going to spend the rest of our lives" — is often held up as one of Wood's classically clunky lines. In actual fact, Criswell used that as the intro line for his TV show for several years before Plan 9 was filmed (and continued to do so afterward), though he usually gave it a much wryer delivery than he does in Plan 9 — witness it in action in his appearance on the Johnny Carson New Year's Special in 1966.
Bela Lugosi grows about a foot and hides his face behind a cape when his body double takes over, and we're not supposed to notice.
Woolseyism: The fact that some subtitled and dubbed versions have better writing than the actual movie is less of a show of the translators' skills and more damning evidence of the movie's own ineptitude. Just being able to truncate the redundant dialogue and make some phrases sound much more natural is an improvement already.