Yes definitely worth it - the dressage is a little bit more testing (and has usually better judging), the showjumping is 1.15m not 1.10m and the cross country often has more combinations. Depending on where you go also, the showumping can be run as the last phase - great practice for a CCI* On...
Definitely do both. Life is far too short: squeeze as much as you can into one day. Just dont fall asleep in the soup !!
"Nothing is worth more than this day" (John Wolfgang von Goethe).
Mine did similiar thing - (although not as bad) and I had a mirror put on the partition and he has been really good every since. Seemed to reduce the stress when setting on and arriving.