Hey Anthony,
Would it be possible to replicate the switch mechanism found on those light-up Gundam heads? IIRC don't the Gundam heads use a "magnet" switch, where you can turn on the lights by passing a magnet over the head...if it's possible perhaps that would keep the original look of the VF heads.
I'm not sure how feasible it is, but you might get away with one mold for two options...one with lights, and one without for those that just want a straight recast.
I guessing some would have reservations of how the head would look if there was a switch in the back.
I would like a VF-1S head with all the bells and whistles....light-up visor, hollow metal head lasers. And I think that hologram backing behind the visor would be a very nice touch.
The ultimate would have you make the heads such that a talentless oaf like myself wouldn't have to do anything but pop the old head off and put the new one on to have that "I just customized my valk" look.