I've been thinking that the only way to solve Balance Druid mana regen issues while preventing run-away regen once we gear further is to make Moonkin rely on Dreamstate for the entirety of Cataclysm.
The constant (but inevitable) comparison is the Elemental Shaman given the classes' hybrid caster-healer commonality, but I believe that Innervate is the single spell which is preventing the Balance Druid from having mana be as much of a non-issue as Elemental Shaman.
Euphoria - By buffing Euphoria (to say 24% or so), the Balance Druid will eventually gear far enough that a self-cast Innervate will no longer be required for sustainability. This will lead to the Balance Druid eventually becoming very desireable to stack, ultimately being not the way to buff Balance mana regen.
Innervate - By buffing Innervate itself (even if by a Balance talent), again Moonkin will suddenly have a powerful mana regen tool to throw out in a raid. Even if required to keep self sustainability, the boon of having the option to essentially drain oneself to give a load of mana to a healer is too powerful.
Dreamstate - By buffing Dreamstate so that only the Moonkin is gaining significant mana from Innervate is the strongest way to assist the Balance Druid's mana regen without letting them ever have it free to cast on other players. Any other form of mana regen leaves Innervate open to future issues where they outscale the necessity for it being self-cast.
The current issue is that a Balance Druid is typically oom well within 3 minutes with a very basic rotation. Therefore, perhaps the following would be an appropriate incarnation of it.
When you cast your Innervate on yourself, the cooldown of your Innervate is reduced by 90 sec and you regain an additional 15/45% of your mana over its duration.
These numbers are very debatable and very likely doesn't require a double buff, but I feel a change along these lines is the only way to guarantee that Moonkin do not oom from dpsing, which includes Starfall, Typhoon, Moonfire and utility spells.
In my opinion, the only time a hybrid caster should have a very real risk of oom is if they are healing. This appears to be true for the other hybrids, as it should be.
I don't wish to be another 'oomkin' for Cataclysm (including knowing that we'll eventually receive 'bandaid' fixes to keep us in line) and would rather see other factors be what limits our potential. There are other issues with Balance, however, this is one that has been around for a very long time in some form or another.
Fellow poster Karadrum followed up by pointing out the pointlessness of having Innervate so strongly bound to the Balance Druid's regen. It makes one wonder why Innervate is even able to be used on other players in the Cataclysm environment when it is so very necessary always to be cast on oneself. This is what will continue to be the bane of Balance Druid mana issues without careful change.
What the future holds...