Soul of the Dead, Illustration of the Dragon Soul, DMC:G. Pick any two and you're BIS.
Admittedly, the proc doesn't affect Divine Plea unless you're timing it (and with the nerf, there's more incentive to not just burn every cooldown). But it /does/ affect Replenishment (and remember, Blizzard is explicitly designing raid encounters around its availability) snd active regen through Seal of Wisdom. And the added spellpower and crit count whenever it procs (and, incidentally, help to make up for the DP nerf when you do pop them together).
You can also get it for a lot less than 10K if you: (1) are not in a hurry and buy the individual cards, and only when they're at a heavy discount; (2) are an herbalist and are/know an inscriptionist - it takes a half hour to farm the mats for one Darkmoon Card of the North, and with a little luck you can get a few Nobles for a relatively small investment before hitting the AH as in (1) to fill the holes.
A huge investment, sure. But you get what you pay for. Even without the proc, it's competetive with the likes of the badge trinket (one point of int is a few times more valuable than a point of SP).