party1 can be anyone in the group, I don't know who needs the heal based off that... I commonly threebox or fourbox with a live player in slot 4/5 so being able to heal them would be nice...

I have macro's to target my players and cast appropriate spells, but short of editing all these macro's when I have another player in the party...

Same thing applies, once you have this covered for 5 players you dedicate 20 buttons on an x-keys and you can heal a 10 man raid where before you could only heal a 5 man...