New Voltage

The life expectancy of the filiments in the lights won't be appreciably shortened by the dirty DC signal. If you don't notice any ill effects or flickering in the bulb output I wouldn't worry about it.

Alex's original post was that he had an issue that he was seeing 12-13 volts at the fuse panel with the lights on and 14 volts with them off. I am assuming that he had 14 volts when the lights were on or off before adding the relays. That being the case then by moving the light load to the alternator output terminal is some how (bad ground, bad connections, etc. somewhere in the system) causing the voltage regulator to not be driving the alternator enough to ensure there is adequate voltage in the system.

Good engineering practice tells you to provide common points for providing power and grounds (that's one reason why you don't see accessories powered from the alternator from the factory). It eliminates all kinds of weird issues that come up from ground loops and multiple connections. If you have a concern that the charging circuit (the issue with inadequate wiring throught the light switch has altready been addressed by the relays) through the fire wall is not adequate to deal with the 9 amp load the head lights add to the system then you would be better served to fix that then put what I would consider a bandaid on it by taking power from the alternator.

IMHO, if you have dim lights due to old wiring and you are not add lights that draw additional current then the correct thing to do is fix the wiring. The factory wiring is quite adequate for standard sealed beam bulbs.