Hi,
Are you regularly winning or placing in the top 3 of your Junior races? If not and the Junior races are important (as you suggest) for going to a USA Cycling Junior Dvelopment Camp, then I would not ride the Cat 4/5 races.
If you are cleaning up in the Junior races then you might want to do just the Junior race on Saturday and both on Sunday for the experience and training.
As for your training over the next 1-1/2 weeks, if anything I would taper a bit before the races if these are key events. If you feel like you are not adequately trained then do only the Junior races and keep training at your current intensity.
Hope this helps. Good luck.