[PhoenixAzul]

BlueEyed,
Typically, I'd give you my "being local is awesome" speech. But in your situation, I'm not going to.
My own local sorority has flourished because we have an established system of locals, both fraternity and sorority. Your campus lacks this tradition/establishment. There's not really any history for you to lean back on for guidance. That can be great in terms of making progressive decisions, but it can be bad because it leaves a lot of room for bad influences to sneak in. (Basically, because the bushel is so small, one bad apple can really ruin the batch!).
The NPC (and NPHC and Multicultural) sororities have a lot of resources. What you'd gain is guidance, insurance, structure etc. Downfall of this is that you won't have the freedom of direction that a local would, but you'd have a framework for construction.
The downside: no guarantee of colonization. Dues will go up (pretty exponentially, actually). You're going to have to sell that to girls on your campus...which means push the networking benefits of national sorority life and etc. Loss of your letters (but you can include that in your chapter history).
I think that the presence of a national organization at your school will be a nice "anchor" for a new system...its a rough life as a local sometimes, and even more when you're the only one.

Good luck.