Your experience is that most nurses are LPNs? Do you live in a nursing home?
I have always worked in a hospital setting (been a RN since 1992). While our LPNs are grandfathered, they don't seem to be hiring any more. We have two of them on my unit. Of course, we also have about 34 others who are all RNs.
As for educational preparation, I have an associates degree in nursing (ADN). Maybe half of my peers at work have the same. I earned it in two years. BSNs generally spend the first two years leaning liberal arts stuff, then start with the clinical nursing curriculum during their third year, completing it all in their fourth year.
Irregardless of how one earns a degree in nursing, we all take the same national exam. These days it's all computerized. There are not different scores acceptable for different states. You either pass the NCLEX or you don't. The days of different scores required in different states ended before I became a nurse. My mother remembers those days though... but then again she's 80 and remembers when Wyatt Earp died.
Once you pass, you can apply for licensure to individual states. One of the Dakotas requires a BSN to go along with the NCLEX but as far as I know that's the only one. Several states belong to the Nursing Compact, where a license from one can be used in any of the others (similar to a NY driver's license being acceptable to drive in Connecticut). Most of the states require their own license for practice. If you move from another state then it's just a formality to get that state's license (requiring 2-3 weeks of wating and a check). Generally speaking, a license from any one state will qualify you for a license in any other state.
They pay us the same no matter how we were prepared for the NCLEX. I've heard of places that might pay 25 cents per hour more for a BSN but I've never worked in one. Work experience (as a RN) has much more influence on what rate you're paid. I'm making roughly double what I did when I first graduated now.
As for demand.... man, it's a seller's market these days, and the nurses are what's selling. 3-10 thousand dollar sign-on bonuses are the rule in my neck of the woods. We don't grow on trees any more, though the jobs sure do.