I've suggested before that if clerics without spells appeals to you, but you think the random chance of success rolled for every prayer seems too extreme, you could mix the technique with traditional cleric spell preparation. In other words, the cleric gets a small number of spells that work without the need for a reaction roll, after which they have to trust in the gods.
I think I'd like something halfway between "standard cleric plus off-the-cuff miracles" and "roll for every miracle".
So the idea I have now is: At the beginning of an adventure, a cleric can pray at a shrine, church, or temple to pray for a number of "guaranteed divine favors" (bonus spells) equal to half their level, round down. This is over and above the open-ended call for a miracle. Thus, a 1st level cleric is the same as in OD&D (no spells,) but has the possibility of prayers being answered, so the class is slightly better at the low level... but an 8th level patriarch only has four sure-fire spells, with everything else covered by divine whim.
This "spell prep" can't happen during the adventure, unless there's an appropriate shrine, so guaranteed spells don't refresh every day. You use all your bonus spells, you have no guarantees of further aide, although you can still ask. Thus, the bonus spells are more or less per week, rather than per day.
I, personally, would roll for reaction when the cleric has his "shrine time". On a bad reaction, the gods are displeased or the cleric's faith is wavering: the last bonus spell the cleric casts doesn't work, and all requests for aid. On the worst possible reaction, the gods are angry or the cleric has lost faith: the *first* bonus spell the cleric casts will fail, and no other requests for aide will work thereafter until the cleric does penance or performs a selfless service on behalf of the church. The player won't know the result of the roll until crunch time.