I used my own spontaneous casting cleric-like class in my first D&D campaign, and it worked really nicely (even while being much more limited than yours).
Basically it was called the Prophet class, and it had two domains, cleric BAB and saves, but learnt spells and cast spells just like the sorcerer (and used Cha as key ability, just like the sorcerer too).
The 3-4 spells known each spell level were called the 'faiths' of the prophet... the things he had faith to call upon. Frankly, giving them such a restriction was no worse than giving sorcerers that many spells known each spell level. I can't see why your example (or the favoured soul example) layer so many other benefits over and above what the poor spontaneous casting sorcerer gets!
My prophets were, like sorcerers, relatively weak until about 6th level, but once they reached 9th level or so they seemed like powerhouses that never ran out of spells (just like sorcerers).
I'd play one in someone elses campaign in a heartbeat!
Cheers