Accuracy chests should only rarely be needed - for high level arena or hard Doom Tower, you may need a few of your key debuffing champs with accuracy of 350, 400 or even more, which means you'll probably want an accuracy chest indeed. At your level, I'd say only as a last resort since you generally need hp/def/attack percentage as chest main stat depending on the role of the champion - mainly you should get accuracy from substats, accuracy banners, set bonuses and GH upgrades. Accuracy auras are an option too, but the general idea is that it's easy enough to get sufficient accuracy from other sources, so your aura should be something that adds more value - mostly speed and defense, but sometimes also HP, attack, resistance. In your case, you'd want Ignatius' aura for your CB team.
In dungeons up to level 20, the rule of thumb is you need +/- 10 times the stage number as accuracy, plus a little bit. So for Dragon 16, you'd need something like 170 to reliably land your debuffs - with only 120, it'll be hit and miss, landing some but getting many resisted as well. For CB, it also depends on which difficulty you hit, but for UNM you'll need something like 220-230 - which is a good place to aim for in general, as it will also work on top level dungeons, faction wars, most of normal DT and in arena against most opponents except the ones that really beefed up their resistance.
Middle of the road for everything in terms of stats won't really cut it anymore going forward. Your nukers should really go hard for crit rate, damage, attack (or whatever stat determines their damage), plus of course speed and if relevant accuracy. Support champs go for survivability all the way, never mind their damage output. For key debuffers, yes, accuracy is worth sacrificing other stats for. That makes Kael a little tricky to gear, because he's a nuker in arena and on dungeon waves, but a key debuffer on CB and the dragon itself - it's entirely possible to build him with sufficient accuracy while also having good damage and speed, but of course it requires better gear.