The problem with this degree of focus, as Jonah Lehrer would tell us, is that moments of insight and genius come in the shower, on walks, doing hot yoga; when the mind is less focused and allowed to wander. Konnikova makes the same point: "Creative insights and imaginative solutions often occur when we stop working on a particular problem and let our mind move on to something unrelated." Overstimulated, the wandering mind's creative potential could theoretically be diminished.
She also notes, though, that caffeine "boosts energy and decreases fatigue; enhances physical, cognitive, and motor performance; and aids short-term memory, problem solving, decision making, and concentration ... Caffeine prevents our focus from becoming too diffuse; it instead hones our attention in a hyper-vigilant fashion."
As someone who works with a lot of self-described creative types, my experience is that the most common barriers to creating are initiative, commitment, and self-doubt. Caffeine helps with all three of those. Even if there is some sort of subtle effect on free-association or Rorschach inkblots, or some people overdo it and lose sight of the big picture in a euphoric state of hyper-vigilance, I can't see that outweighing the benefits of stimulation, disinhibition, and improved ability to focus on work. Deferring to Woody Allen: "80 percent of success is showing up."
How all of this comes together to make any one of us think differently varies, of course. Case studies for caffeine endorsement abound: Simone de Beauvoir, Beethoven, Gustav Mahler, and the famous example Honoré de Balzac, who "is said to have" had 50 cups most days. He was plenty creative, but was also a notoriously eccentric man with gastric problems who died at 51 of a cardiac issue.
If you're taking in enough caffeine that it messes with your sleep, the benefit can definitely be negated. If you become so motivated and vigilant that you spend hours perfecting every aspect of basic tasks, neglecting others, or your own relationships or hygiene, or not exercising, all of that is also no good. Like every drug, its effects can't be considered in a vacuum. Like all good things, moderation. You can't get too much moderation. "Fear can sometimes be a useful emotion."
Auden's best work came out of his Benzedrine period, but few who take hard stimulants become Auden. Adderall and caffeine likewise focus the minds of different people in different ways. A nice thing about caffeine, though, is you can legally experiment with it on yourself and your friends. If you don't have any precluding medical conditions, take a Red Bull or Full Throttle or Neurogasm or two, and then try to be creative. For example, name as many hypothetical new energy drinks as you can in, say, 14 minutes. Then test yourself sober. Another good prompt might be, why did 25,000 bumble bees die last week in a Target parking lot? Be creative. Think of as many answers as you can.