To you it might seem dumb but in theory if abs-acc is anything like the other abs spells you should be able to get 20-21acc. So I see no loss, and there is also abs-dex if your acc fails even more.
As for plastron its not just for a "couple of points of str/att" drk isnt an auto att job like war or mnk it also has a magic side thus the need for full time refesh, you dont wanna be full timeing parade gorget.
With a rdm in the pt I have plastron, prade gorget (when i'm not fighting), and santion refresh(not tring to save money on food duration)+ the spell Refresh = 6mp/tick.
W/O that I see many drks who cant even keep up with casting spell thus in the end lowing their over all dmg.
And w/o even a drk magic set up dont expect to even see 90-110+ mp aspirs as well.