Steve & Vicki,
Great that you're now Escapees! Maybe I can help on the matter of the parks, as I found it confusing at first, too.
There are 4 kinds of parking options for members, as described at the web site:
http://escapees.com/ParksandParking.asp. You've got the discount park program figured out - these are parks open to anyone but they offer a special discount to Escapees, usually 15% off the daily rate. Note that sometimes they require cash, not credit cards, to get this discount. Also, if you stay more than a few days the weekly or monthly rate will be less than the 15% discount gives you.
When visiting any of the other three type of parks, for the purpose of just traveling through the areas, there's virtually no difference between the SKP Co-ops, the Rainbow Parks and the Escapees Rainbow Parks Unlimited (ERPU), which are simply a combination of the Co-op and Rainbow Park ideas for those buying a lease. Only Escapees members can stay in these parks, and you'll be required to show your membership card when checking in. (Then you'll get a SKP Hug.) Each park sets its own policies about reservations (most don't take them), but it's still a good idea to call ahead the same day to see if they have space. They also set their own rates, typically $2.50/day dry-camping (1st day often free) and $9-15 per day FHU. Policies and contact info can be found in the printed directory that you should have received.
Unless you're interested in spending significant time in one area, you don't need to concern yourself about the differences among the 3 kinds of SKP parks at this point.
I've stayed in 3 Co-ops and one Rainbow Park, and I've visited 2 others just to check them out when I was in the areas. I was able to get a site each time except when I arrived a half-hour after the office closed (Saguaro, Benson, AZ). I could have boondocked, but the cold weather in November (27 degrees) dictated that I needed shore power, so I went elsewhere. I only called ahead once to be sure space was available, when I discovered there was a fair happening that weekend in the area. The personalized welcome and friendly support I received each time was unequalled by any other place I've stayed. SKP parks are always my first choice whenever I'm traveling, then I go to my other directories when I'm not able to fit them into my itinerary.
I hope this helps.