While that's something to think about, keep in mind that the level of correlation between those voxels is ridiculously high. Simply adding more voxels isn't necessarily adding useful information. Even more so, fMRI is based on the BOLD effect [1], which is highly blurred across a fairly large area. While there is potential for improvement, there are a number of pretty fundamental limitations to this technology.

[1]: http://en.wikipedia.org/wiki/Functional_magnetic_resonance_i...