Food would certainly be awesome, or heck even an enhanced version of Wyvern Feed. I mean come on, this stuff heals what, 60 HP?
That said, while being able to heal our wyverns easier would be awesome, I think some form of passive -PDT would help far more in the long run. I don't think it would unbalance things much at all to increase survivability at least a small bit. Avatars already have this in the forum of -50% PDT, and all a SMN has to do is release/summon and they have a brand new pet at 100% HP ready to go.