Playing a nuker caster at higher levels is problematic due to the very high saves on pretty much everything. That's perfectly fine by me as I no longer carry too many instant AOE spells anymore anyhow. What really bugs me, and I only realise this when I bother to dust off my toaster sorc is the capstone. I just never use it. The cost outweighs the benefit by some margin in my opinion. When I am getting pummelled from pillar to post in epics, being able to self heal is paramount.
My suggested solution is a simple one.
While in Elemental Form, you take NO DAMAGE from your element and are instead HEALED by your element. However you take double damage from your opposite element. Think the way pale masters work with negative spell damage, vs light spell damage.
If the heal portion is too much (due to nuke power), then make it a useful percentage of the damage value. Worse case, maybe even consider making it scale with your heal skill, and boosted by heal amp. At least that is something rather than nothing.
There you go. Even fleshies benefit from something like this. Also and extra reason to stay PURE.