Google "Intel knights corner"
And you will see why more cores make a difference, the project started by attempting to place 48 Pentium 1 processors on a single "chip" there is another company that did 128 cores before Intel publicized the 48 core project. Knights Corner is the new/next generation version, at 22nm die process. Pretty cool, 50 cores on a credit card...
However, higher GHz rating had always ruled on the overclocker's websites, over multiple cores.
I also agree that currently there is no need for more than 2 cores on a phone.
when the Tegra 2 launched, Nvidia said the "Kal 'el" would support power modes that would make it use less power than any current CPU add it could power off unused cores and only activate them when a certain threshold was met on the currently active ones. Also, if the multicore kernel modules are loaded in Android, the OS should do a Perry dan good job of utilizing the architecture regardless of how the programmers write/wrote their code.
One other thing, no sd is a killer for me unless they provide massive internal storage, as I find HTC phones work much better with an sd-ext partition on a fast sd card.