Alright, though I do also think we should consider application. User increasing their Accuracy is good on paper, but let's remember who these user's are: Staryu family, Chinchou family, Volbeat, Watchog, and Morelull family. Aside Staryu & Chinhous family getting more accurate Hydro Pump, Thunder, & Blizzard, Watchog getting more accurate Hypnosis & Iron Tail, & Morelull family getting more accurate Sleep Powder there's really nothing else they can work with, heck Volbeat doesn't get a major benefit at all (yes, Volbeat isn't a great example and, yes, they have plenty of 90% Accuracy moves like Thunder Wave, but all of them have movesets they work with that doesn't take them getting increased Accuracy into account).
Meanwhile, if its the opponent which gets their Accuracy decreased, that gives them a little more utility. While it helps them dodge their opponent's attack, it also helps their teammates whether from switching it out or in a Double Battle (heck, if they have it work like Intimidate and both opponents in a double battle get their Accuracy lowered that's even better). Or, it could force the opponent to switch out, also helpful in possibly clearing a threat for one of your other Pokemon you want to be out.
I guess there is the option of it also increasing an allies Accuracy in a Double Battle, but that'll mean you'd need to keep them out. No problem for Staryu and Morelull family, though I don't think too many would be too keen wanting to keep out a non-Drizzle Lanturn, Volbeat, and Watchog. Just look at Power Spot, great Ability but no one wants to use it because Stonjourner falls over from a Special moves, especially if its a weakness. At least if it decreased Accuracy you could then recall the Pokemon after it blinds the opponent.
