In regards to the new instruments, I almost feel like crying for the relic horns out there. Comparable performance can be achieved by having the AF3 and the Cythara (not that MP regen while inside abyssea matters a **** anymore). Problem with that harp is that if you've kept your stringed up to date, the range on Ballad2 is a pain in the *** if you're in a mixed party, but a godsend if you're in the manaburn party. Also helps with Ballad3's pathetic range.
In regards to the finale instrument, I'll just say it's a placebo effect, but it is also much more useful than string. I used to own a Military Harp, since I got Finale, and it was useless, got resisted way too aften (I kept both skills capped with besieged), much, much more than wind instrument, so I promptly sold it (also, lol ridiculous price tag on it) and have casted Finale with I.R. Horn with little to no resists whatsoever since.
Now, stringed Mazurka is good for both the +3 on duration and AoE range, since more often than not people lose the move+ because they stray too far and take long to stap back for the cast, and we all know how they beg to run faster.
Haven't used prelude in forever though (maybe could be useful with an inverse JA to Pianissimo in a ranger party), Minne+3 is useless, Elegy +3 is worthless as well, it will cap on enemies at 50% regardless and if you can't land it within 2 or 3 casts, means youredoinitwrong or the mob is very resistant. Madrigal and acc in general is lolstatus atm with the lack of 85+ content requiring it, but that Minuet+3 however, might be helpful coupled with Minuet merits, although it won't make-or-break you if you don't have.