ORAC, having had the chance to work with AC-130's (spooky and specter) in the past, I won't comment other than to observe that it is used for particular missions, and is not a "one size fits all" asset.
The J model is simply the upgrade to the C-130 J family ... but of course the mission systems people wanted upgrades too.
When it is called for, I expect the J to do just fine. Nice capability, and as Evalu8ter pointed out, some distinct advantages for particular calls for fire from the ground units.