We have 4, and I don't think fitting things with 8 would be any harder for us...the bigger your traveling group, or the less space you have per person, the more ruthless you become regarding what you're bringing, which makes packing simpler.
We're planning for another baby next year, and don't anticipate packing becoming significantly more complicated. Diapers, clothing, stroller, bassinet, will be constant. I think the biggest changes will be needing another car seat in each van and needing another portable bassinet. :O)