I use void mainly because I like the style. The toons look cool and vicious. Skulls and demons are just cooler to me than fat Rock rollers and punked out chemical tossers. Most people don’t care about style or looks they just play meta cards like BD and Rocks.
My suggestion is to give faction bonus. So if player plays multiple cards of the same faction they get a bonus, the more faction, the more bonus. What’s the point of having different factions anyways? There is none. They all just minions at this point.