NCDC isn't that much different than the old Premier division. Just looking at the commits page shows a pretty clear trend in a lot of players choosing to play NCAA D3, albeit some of those schools with NCDC commits are pretty close to D1 hockey, like Norwich, Endicott, Geneseo, Utica and other high end teams with some D1 transfers. I think it's the draw of increased or more stable playing time for four years, in front of still packed houses, and at cheaper schools pulling the kids in and there's certainly been a massive increase in quality of D3 hockey over the last decade.
For expansion, the NCDC announced for next year is growing to add the New Hampshire Monarchs, probably a prearrangement made with their switch from EHL to USPHL. Assuming no NAHL teams fold or get added (and the one that is dormant returns), that will make 24 NAHL vs 12 NCDC teams. I doubt the NAHL will expand, although look for them to relocate their East Coast franchises to places where people actually will watch junior hockey.
Trying to compare the two is asking for trouble since their turf war is heating up. The measuring stick is and always will be "how many commitments and where." Having watched both leagues, the NAHL-NCDC are pretty comparable: they both are watered down from competition with each other and Canadian tier 2, have kids on the ice who aren't as good because of daddy's connections, and have massive drop-offs in talent from the top to bottom of the leagues. That being said, I have to give the NAHL has the upper hand (at least for the first year of free-to-play competition) with the NAHL edging out the NCDC simply because they commit more kids to D1 schools per team.
It's a shame that since war was declared the NCDC will probably never rejoin USA Hockey and have both leagues under the tier 2 umbrella. I'd pay money to see an annual 4 team national championship between the champion and runner-up teams from each league.