How about the idea of learning spells or other magic that require intelligence to use in battle? These could be gained from special books if the creatu has the right intelligence level already. If not, the player could re-read the book to learn the spell later. There could be defense spells, healing spells, elemental attack spells and what not in addition to normal creatu attacks.
You might also be able to get weapons or items with magic in it that requires intelligence to unlock as well. The most basic spells could be unlocked with the amount of common books available. I'd like to see such magic given to the planet swords and scythes.
And if someone wants to go beyond that with the rare, retired books, its the work of only a few moments to find out who has more books and ask them to train their creatu in intelligence... for a price of course. They don't need to actually own the book themselves.
I like the age factor, but how would that work with rays? Do they loose a point every time their age is changed? Don't like that idea. And we really don't want highly intelligent babies running around either. I'd say open a public library where creatu can read books instead. A person could read one book a day, even if there isn't actually a book out there for the creatu to read. This way, dedicated daily trainers have the advantage, not just book collectors.
Plus, it would solve the problem of my idea to open an academy on every planet. Each planet could have one responsible for training each stat. Say, Relcore could have the public library, Atquati could be responsible for defense, Scria could be responsible for agility, and Reiflem would cater to those who want for nothing but power. ::chuckles::
And I would also suggest that the price start out somewhat low, but increase as the creatu's abilities increase by, say, 10 points. This would keep the ranchers who train in business as well as their costs rise, but allow everyone some ability to train.
As for levels, yes, we should be able to rank creatu by questing or battling. Don't know if I want to lift their levels JUST with fighting. Fighting isn't all there is in order to gain knowledge and rank, and is a very pokemon concept. Perhaps there could be creatu councils for each planet, and a creatu could go to the council of the planet they originate from to participate in a quest or rite of passage that allows them to advance in rank. Or they could obtain field promotions after a certain number of other creatu are defeated. Both would be best, but if I could choose only one... quests would be my desire.
We definately do need more ways to involve creatu in the Res gameplay. Right now most are just hatching and collecting them like trophies. That doesn't suit my taste much, and if Rescreatu wasn't otherwise such an interesting concept, I most likely would have gotten bored and skedattled. The gambling aspect of hatching is definately a plus in my book.