Which is better, overall? Is one more minion worth having more than 25% damage? --- Remember remember... the 30th of November. The day that heroes could not save the world. ~In remembrance of City of Heroes.
Don't forget that Spooky Armor has 8 less defense. Also, Spooky Armor's set bonus and it's innate minion damage increase put it at 28% total increased minion damage (11% per piece on Spooky vs. Tiki's 10% each).
7 minions doing 27 + 30% damage (base damage of Pygmy Staff + total minion damage bonus of Tiki Armor) = 245.7
Let's assume you have a Mythical Pygmy Staff with only 15% damage increase.
15% for Mythical Prefix, 19% for Hercules Beetle, 14% for Scroll, 4% for Necklace, 14% for Destroyer, 16% for Avenger = 82% before Armor bonus is factored.
Tiki with all bonuses = 447.93
Spooky with all bonuses = 429.3
Now, this is assuming Destroyer and Avenger affect minion damage (I have never checked to see personally if it does). However, even if we were to assume it doesn't, the result is something like this (and far more realistic anyways since the maximum damage setup severely limits mobility) -
Tiki (minus 22% for no Destroyer/Avenger Emblem) = 406.35
Spooky ("") = 393.66
TL;DR - Initially, Spooky does more damage at the cost of defense without all % damage increases. However, as you get more and more damage, the 7th minion starts to trump the raw damage Spooky provides.
Bear in mind, this does not factor in defense, so Spooky may end up trumping Tiki. (Also, it looks cooler, imo.) --- /target Face /cast Palm
32 base damage + 15% (Mythical Prefix) + 55% (Tiki total) + 60% (Accessories bonus (no Destroyer Emblem/Avenger Emblem) x 7 minions = 515.2
32 base damage + 15% (Mythical Prefix) + 83% (Tiki total) + 60% (Accessories bonus (no Destroyer Emblem/Avenger Emblem) x 6 minions = 495.36
Individual damage of Ravens using Tiki Armor is 73.6. Spooky Armor is 82.56
Overall, I would still lean to the Tiki Armor, but without extensive testing in various environments, I can't give you an objective, "One is clearly better than the other." answer. Tiki Armor's more minions means more damage on softer targets, and more attacks for chances and knockback and also for reseting certain enemies from firing (like the Caster minions in hardmode dungeons, or Paladins).
Hope it helps (also, if someone found a flaw, please let me know) --- /target Face /cast Palm