^Even the cellular level of detail would be unnecessary once we figure out how brains encode and process information with cells (moving from the physical hardware to an abstraction of a machine, even sets of equations that describe an odd analog circuit, and finally a description of what that circuit does).
But then we wouldn't need simulations, we could get much better results by building synthetic brains that behave on a hardware level fairly similar to the real mccoy.
Well, I guess that would be the point, along with perhaps mapping a human brain onto the new hardware so people think
they're upgrading to a new, improved physicality.
Even a fairly rough copy would probably do fine, since people are constantly forgetting, misremembering, getting hammered, and getting in wrecks and we still have little trouble accepting the continuity of their existence. For most, it would probably be less of a behavioral change than sobering up, finding Jesus, or surviving a date with Lindsay Lohan.
One step in this process might be getting a good enough copy to run, after which the copy could be monitored with vastly more precision than something like an MRI scan of the brain. Then we could start experimenting with how thinking actually works, moving up a layer of abstraction so we can design a better brain, or understand how to just add knowledge to an existing one at the core level, instead of trying to "teach" it via external sensory inputs, leading to "I need a pilot program for a B-212 helicopter."