Are we talking regular spell list + domain spell as spontaneous caster? Sounds pretty hinky but it's hard to directly categorize the benefit as it continues to become more powerful as the cleric gains levels. At low levels 1-4 it's likely only worth a +1 LA but as the cleric improves it becomes rather significant.
Also the determination would depend on whether the cleric could use spontaneous metamagic which would be a massive increase in power.
Throw in feats like divine metamagic and you could easily have a very significant increase in power at high levels.
Honestly I'd be very reluctant to do this for one class without basically doing it for all spellcasting classes. Of course if you bump up the spellcasters who arguably have it better than the rogues and warriors then you bring the game very much out of alignment.
In short only do this if you are willing to rewrite all the classes and PrCs to a higher powerlevel.
Also the determination would depend on whether the cleric could use spontaneous metamagic which would be a massive increase in power.
Throw in feats like divine metamagic and you could easily have a very significant increase in power at high levels.
Honestly I'd be very reluctant to do this for one class without basically doing it for all spellcasting classes. Of course if you bump up the spellcasters who arguably have it better than the rogues and warriors then you bring the game very much out of alignment.
In short only do this if you are willing to rewrite all the classes and PrCs to a higher powerlevel.