One last thing, Bless is pretty powerful. I allowed the cleric to spellburn over an entire month of fasting, and melt down several platinum pieces to form a new holy symbol and bless it. Now it's permanently +2 to spell checks... that definitely made the cleric a loooooot more useful.
Wow you were generous. Did the cleric find some kind of ritual to be able to create this magic item?
It's a function of the bless spell... he spellburned a ton of physical stats to be able to do it, and rolled well. If you roll high enough the bonus is permanent. But you can't use the spell again for another month (and I may make it much longer)... and he had to use some pretty expensive materials.
There's some debate about whether clerics should be able to spellburn or not, but ... I don't see the big deal. I made him fast with nothing but a tiny scrap of bread and water for a whole month to simulate the physical withering... that seemed fair.
That sounds like a cool story, so I can't help but think it was a good decision to allow the spellburn by the cleric. The result is essentially a magical holy symbol consecrated in the name of the cleric'c god, I can't imagine the god being displeased by that.
As for not allowing spellburn for clerics... Seeing what it took to spellburn on this spell, I don't see this happening in the heat of the moment during combat. "Hold, Mr. Ogre, I must take a month's fasting to gain some meager advantage against you during our fight." The point being, it's not likely to happen too often.