To those that feel Rattled isn't substantial enough of an ability, why does it have to be substantial? Look at Necturna.
I think the other thing to keep in mind is the lack of potent attacks that fall in the Bug/Ghost/Dark category. There's no Dark-type Draco Meteor or Ghost equivalents of Close Combat or Superpower. We're talking about Bug Buzz, Shadow Ball, and Crunch. While Bug attacks are really only used for STAB, you're dealing with fairly low base attacks, bar Megahorn (with little OU use at the moment anyway.) Shadow Balls and Shadow Sneaks are usually coming from things that desperately need coverage (Jolteon), or do Calm Mind with Fighting/Ghost coverage (Sableye, Reuniclus).
A +1 Speed boost can be potent on whatever we want it to be- it's totally dependent on their stats. Imagine if pokes with stats like Heatran, Chandelure, Magnezone, Vicinti, could get a +1 speed boost by taking a super-effective hit.
This is either going to be a CAP where either an amazing ability covers up his subpar typing, or above-average stats mitigate it. I think valuing the stats are much more important, because, similarly to how DJD mentioned different abilities creating a risky environment, your EV spread creates more than 2 or 3 risky decisions not only in-match, but far before entering the battlefield.