I used Ridemax for the first time in December 2010 and it was a real life saver. I've continued to use it and used it this past December during the super-busy week between Christmas and New Year.
At this point, I'm with Cristin82 in that I can make my own plans on the fly, but I like to use Ridemax to 'model' my plans and make sure I'm on the right track.
However, the software needs some serious updates with regard to MaxPass, since it doesn't account for the fact that you can pull a fast pass now as soon as you are in the park, whether that's as part of MM or EMH, or just part of the pre-rope drop entry time you are given.
Because that first fast pass is usually for shortly after official opening, it really sets you up for being ahead of the curve. And you can kinda-sorta work around it by leaving the attraction that you're going to fp first off your plan, but then you have to make sure you can fit the actual ride in shortly after opening...so that gets a little sticky.
For instance, our first day at DCA - was an EMH day and we didn't have EMH (we had no choice because every day that week was EMH). However, we were close to the front of the line for regular entry, so upon entering the park I snagged fast passes for Incredicoaster, then we rode Soarin' standby (since you can usually get on Soarin' prior to rope drop even if you aren't eligible for EMH). We had time to wait for B1, rode, and made it to rope drop at Pixar Pier with a few minutes to spare. Shortly thereafter (while riding TSMM and PPA) the Incredicoaster passes activated and I was able to pull RSR passes. This put us 2 big rides ahead of schedule as opposed to the RideMax agenda.
It's still helpful for sure, but I found myself using it to get a general feeling for the flow of the day and then coming up with my own plan. There is no way for RideMax to account for picking up cancelled fastpasses either, which can be huge on a crowded day. Flexibility is key.
All that said, your trip at the end of the month with 19 people, yeah, MaxPass is a bit much (but maybe have one person get it each day just for the photos!), and I think Ridemax will suit you just fine as a planning tool since the parks will not be super packed. It's still a great product and I enjoy using it to plan out scenarios.
Have a great trip!