Use a RC circuit to store energy for the solenoid, then you can sustain the solenoid with much less current when the capacitor has pulled it in.
I think you need a very big capacitor to be useful in this case which is not practical. These solenoids suck current like hell man, I once remember doing a door keylock for my son's room and i used a small solenoid taken from old cassette player, it refused to move with a transformer rated less than 12v 500ma.
Your ideas are great Steve and definetly worth experimenting with.
Regards
Mahmood