To back up one of Farsight's comments, I too find the RNG for the quest rewards very streaky. If you get one bad box of loot, chances are you're next few are going to be bad if you do them right away. After a couple weeks of farming this quest, I've learned to just be patient... If I get a box with terrible rewards, I'll just wait about an hour before I try again.
Weapons are usually the best items from the strongboxes. You can get pretty decent PvP weapons from the quest pretty often, and you'll also be teased a lot by a weapon that is one mod short of being perfect (like an ornate axe with 42% DI, 30% SSI, 57% ML, and then spell channeling/-1... oh why couldn't that spell channeling be stamina leech instad?!?!?!?!). Armor is usually junk, the best you're probably going to get out of armor in the boxes is meddable 18+ LRC items, which are fairly common. Jewels are hit or miss... But you can definitely get some good ones, just luck of the draw. I haven't tried the sanctuary quest yet, though, so I'm going to give it a few tries this weekend and see how it compares.
A question to some others, though: Do blue healers drop the map fragments as well? I've only ever heard that red ones do, so I've never bothered trying the blue healers; but if they do drop them, it'd make that step go by SO much faster.