CONCACAF don't deserve more spots than CAF. They already scrape the bottom of the barrel with four, Honduras are useless. Africa is a deeper confederation. USA, Mexico and Costa Rica may have done better than most African teams at the World Cup recently but those are the only CONCACAF teams capable of doing anything. The pool of teams who miss out in Africa is stronger than the likes of Panama, Jamaica, Haiti, etc.
Granting any more spots to CONCACAF or CONMEBOL will drastically dilute the qualification process in those confederations. If they're going down that road I think they should unify the qualifying for those two. The one or two South American teams that would make it would be a damn sight better than adding two or more CONCACAF teams. Mexico and USA would probably still qualify and if they can't beat out the weaker teams in CONMEBOL then they wouldn't deserve to anyway.
Of course, this is speaking strictly from a perspective of merit, which won't be the whole basis for any expansion of the World Cup.