Just played around with every piece of Arcane equipment more. Abusing poor Crows and the Cane guys outside the Cathedral Ward in NG+. Not a single one of the damage ones could even kill a Crow.
Damage Items (All have S scaling):
Tiny Tonritus (25 Arc, 6 Bullets) - Shoots out a Pillar of Lightning in a straight line. Did about 443 per hit on the Crows, highest damage per hit. Has a decent range.
Augur of Ebrietas (18 Arc, 1 Bullet) - Shoots out a bunch of tentacles from you in a straight line, kind of short range, hit the crows for 233 per hit, and it has a very small knockback.
A Call Beyond (40 Arc, 8 Bullets) - It has a long and easily interruptable cast time and shoots out a bunch of Lasers from you in various directions, about 2-3 go to your locked on target. The others tend to hit absolutely nothing. I think it was doing a little over 200 per hit of the laser. Might be okay on an Arcane weak boss with a large body that all of them can slam into? Difficult and expensive to use.
Executioner's Gloves (20 arc, 3 Bullets) - Shoots out 3 Black Orbs that did around 190ish per hit on the Crows. If you're too far away when firing it off they'll just do nothing. They seem to hit as long as you're able to be locked on though.
Damage of course, isn't the same per enemy. It was doing far less to the other mobs in that area, making the damage items even more useless in general.
Non-Damage Items (No scaling except Choir Bell ):
Beast Roar (15 Arc, 2 Bullets) - Knocks enemies back, for a split second, and has an insanely short range. Useless. The stun on the Blunderbuss is much longer.
Choir Bell (20 Arc, 10 Bullets) - Heals the same amount as a Vial, but has the highest bullet cost at 10. Not sure on the Range on it for a group heal. Going by the other items, probably super short.
Messenger's Gift (10 Arc, 1 Bullet) - Turns you into a little note messenger thing with one movement speed, but doesn't actually camo you from enemies at all. PVP item? Not sure if it masks your name or not. Probably useless.
Old Hunter Bone (15 Arc, 6 Bullets) - One of the two (somewhat) useful items. It turns your Dodge into a Nightcrawler-ish Teleport. Duration is a bit short though.
Empty Phantasm Shell (15 Arc, 3 Bullets) - The second useful item. It gives your weapon an Arcane Buff like Fire and Bolt Paper, lasts about the same length as well. And like the Papers is unusable on Chikage (Katana), Blade of Mercy (Dagger/s), Burial Blade (Scythe), Rifle Spear, Tonitrus, and Logarius' Wheel. Not sure on the Beast Claw, it's the only weapon I don't have yet and haven't tested it. Does not have an "Attribute Bonus" stat, so not entirely sure if/how scaling works on it and the Papers.
So in closing, the only items I can really recommend are the Old Hunter Bone if you like the Teleport on it and the Empty Phantasm Shell for the +Arcane damage buff if you use weapons that it can be applied to. Both only take 15 Arcane and neither of them have any scaling. I cannot at all recommend the Attack Spell-Like damage items, as they do jack and shit and you are better off just buffing your weapon with the Shell for +Arcane damage on Arcane weak mobs/bosses.
Edit - I'd also like to point out that the Rosmarinus, the Arcane version of the Flamethrower, is a far better use of bullets than the Arcane "spell" items if you want Arcane damage as well.