I was fighting 71-74 mobs. I did notice that I saved bloody bolts and shadows with this cute looking hat, comparing to when I did not equip it.
If TW, I could just fight naked, lolz. For EP, I won't even sub nin, i'd go /dnc, put on drain samba and go afk.
for DC-EM, there a very few mobs (mostly only mobs of a job with acc bonuses) that you will not be capped on evasion nude. This is ever more true in signet areas with signet (no EM or lower mob will hit more that 20% in any signet area with signet on).
Even if you were not at evasion cap, the 4 agl = 2 evasion =1% chance of a miss. There is no way to notice a 1% change in evasion rate (even if parsed it would be insignificant until some huge number of attacks).
For ep, /nin still kills faster (even if you never cast utsu (which inturn makes it even faster than usual) that /dnc. Faster = more gil. And a latent regen effect or fov regen will more than cover all the hp you need for ep-tw. (maybe an occasional bloody bolt...)
Denali bonnet on the is gimp for all circumstances outside of solo TA. (guess its fine for TA+MStab as well)
99 THF, COR, DRK, BLM, WHM, DNC