Firstly, you can't determine CR based on a group of monsters. Well, I guess you could, but that's not how we do things. Secondly, healing is only good in-combat under two circumstances 1) It's a huge amount of hp healed and 2) the healer isn't the one taking damage (which is negated by Firstly). If one of those is true, then healing is golden. Otherwise, you're best off not healing unless its some weird cirucmstance.
So, giving a monster access to some kind of SLA magical healing is just going to make it waste its turn under most cirucmstances. Looking at #1 above, the monster is going to have to heal more hp than the entire PC party can do in one round in order to make it worth it. That's a dragon's heal, for example. And, #2 is impossible to gurantee for any singular monster, so it isn't a feasable design goal.
That's why you don't see a lot of healing monsters or buffing monsters. It is so rarely worth more to do either than do an attack that it wouldn't really help the monster. The cleric taking a round to cast bull's strength on the fighter can be worth it, since the fighter gets the benefit of it this round. A minotaur or such doing that to himself just wasted his action this round. A minotuar casting a cure spell on himself this turn just wasted his round.
Since it would have to be so over the top to be of any use, the healing is reserved for the big ones, the aforementioned casting dragons, and a few random creatures like celestials. That's why fast healing and regeneration (and DR) are the method of healing for monsters. No action spent to heal, its automatic.