Hard to say for sure, but I've seen things more like 1 MACC = .8 Skill or so. Really the Wise set offers such small boosts that it's rarely worth it over stats or other things. About the only thing most RDMs will agree on for it is that the hat + body for Dark magic, and maybe maybe maybe body on nukes. If you're intent on pushing accuracy anyway.

Personally, I've come to the opinion that Wise Cap is not what I want to use for Dark magic at least 99% of the time. Maybe if/when I do Bahamut v2 or something the extra accuracy will be needed. For now, IMO Fast Cast or Haste% is preferable since the main Dark magic we use all have pretty long timers. I actually use my Walahra Turban in Drain/Aspir macros because I share the macros with my BLM, but AF hat is nice for that too. Obviously AF is tons better for nuking.

Body, meh, I guess I have a better nuking setup than a lot of RDMs, but still. IMO the +10 INT on Errant is better. Dark magic if/when I ever get an AF2 body, that's what I'll probably use for that due to the same reasons for Fast Cast on the hat.

Pants, hell no. Mahatama > rest, and that's the bottom line. Well, unless you want to waste inventory for 2MAcc on Dark spells I guess.
Nashira maybe, but the main thing I've seen from people who own them says for max skill onry, which is to say hardly ever. 99% of the time, if you can enfeeble it reliably with any amount of skill, you can enfeeble it reliably with 300-310 skill or so.

Really what you want to do most of the time for enfeebling is cram skill/accuracy into as few slots as possible, then go stats elsewhere. Wise in general is so weak per slot it's very rarely worth carrying or using. Similar to Elemental, though for that you do have MAB and such to work with too.

The exception really is Dark magic, which is the bastard child of magic. With that, skill actually does determine your damage caps. So for a complete Dark magic build, you want as much +skill as you can get, and accuracy besides. Which is why the main thing that Wise is really any good for is Dark magic, if you feel that the inventory slots are worth it for a marginal upgrade.

Hmm, good point about Haste for Draspir (although one might not always be able to fire those off as soon as timer is back up). But what about Sleep and Silence, which don't rely on a potency component? I found and bumped up a thread I saw on KI:

http://killingifrit.com/forums.php?m=posts&q=132127

I know it seems a bother, but being in a small social LS for 99% of my FFXI time, it's a pretty pertinent question for me, since time and manpower restraints narrow my choices down to Beret or Cap or AF1 Chapeau. Yigit and Nashira gear is a distant dream, let alone AF2 hat. :(

Well, I think what you would want to look at first is what you wind up doing that would even need more accuracy on spells. Do you do enough of it to make it worth spending the money and using the inventory room to carry another piece? Or would your effort be better spent elsewhere?

Personally, I've used both the Elite Beret and Wise Cap. I didn't really see a difference with either of them, and no longer carry 'em. Sold the Wise cap just recently, actually, and the beret is muled. I use AF+1 and turban, still trying for AF2.

Really it's not like either are that pricey, can always just try them yourself. Either one is a very marginal thing though.

In Dynamis, Sleep timers can be important too. So I think they're still worth favoring Fast Cast for. It can actually go double for say, Dynamis Xarcabard...cause it's the one Zilart Dynamis where spell success isn't practically a given, but RDMs generally go /DRK there and so have one less Sleep timer to work with.

Hmm, well, I think you've convinced me to drop my cute hat. I never really took Fast Cast into consideration for Sleep, but I do remember checking recast on it constantly during the last Dynamis I did. I dunno, maybe I'll still carry it around for Silence, or maybe just for fashion if I can. :x