Doublers are auto-buy for me if it meets 2 of my requirements...
1. Game is decent.
2. Purchasing it will seem to make the game a lot less grindy. If i think even a doubler cant keep up with the shop prices, i never buy them, and usually just delete the game.
Some games it just feels like you're gaining gold, exp, whatever, at a quarter the pace of what you should. Get the doubler and earn at half the pace. Not for me.
I prefer to support developers that are making reasonably balanced games.
Just to point this out, the worst IAP offenders in the AppStore do not have coin doublers. They see this as potentially hurting their profits. Does EA, zynga, whoever made clash of clans offer doublers? No.
I know a lot of people buy them (mostly impatient children), personally I never buy them, even if its a game I really like. I'd rather earn the gold at the normal rate, I see these as cheating.
Most games that end up being at least decent and offer these doublers are usually freemium. That doubler is a way to pay for a game that gives you a premium-ish, less grindy feel.
...Unless you think these types of games should just be FREE coz paying for them is cheating.
Exact-Psience My 2014 Top 10 Games of the Year: Monster Hunter Freedom Unite, Hearthstone, VVVVVV, Battleheart Legacy, Wayward Souls, Bug Heroes 2, Powerpuff Girls Defenders of Townsville, Deep Loot, Monument Valley, Bioshock Honorable Mentions: Traps N Gemstones, Bardbarian, Goblin Sword