While this would change the paradigm from "cast WoF 5-10 times for an assured set of crits" to "target 5-10 mobs with the aoe to get at least 1 per tick", and ensure that an area effect is used for areas, not as the boss-nuker, I'd point out that the reason more than anything else that it's used a such is due to immunities, resistances, and above all else saves.
As such, might I suggest when you do get around to doing this, you alter the "x manipulation" "lineage of x" and "lineage of deadly x" enhancements to also add +1 to the relevant difficulty check for a given elemental spell (reflex, fort, will). That would max out at a +9 for a given specialist, and at least mitigate to a degree the saves part of the equation for alternative strategies, since it seems the focus for the last few patches has been all about alternative modes of play.
Alternatively, if you wish to heighten the utility of symbol spells in addition to the straight up damagers, would you please add a straight-up general enhancement line for DC improvements, similar to the improved spell penetration line, perhaps based on requiring the relevant 2 feats and taking it further from there.
Basically, the notion you folks have been kicking around is not a bad one in and of itself, but taken in the context of the full level range 1-20 with general utility falling off of most spells at the end of that range due to everything and it's dog "saving vs muchas", as my old Dm would say, additional steps seem warranted when that step is taken to balance out the hit.
Thoughts, alternative suggestions for balancing things out?
/snags fireshield