My last campaign was full of these kind of comments:
"Don't forget the +1 for your Bless."
"Does my +1 for Bless count that?"
"Oh, wait, my Bless might have fired off last turn to stop that."
"Can I use Luck before my Bless takes effect?"
So when we started up Dungeon Fantasy back in 2011, I said, flat-out, we're not using Bless. You can't learn the spell, and NPCs won't cast it for you or on you.
Curse, I left alone. It's a thematically appropriate spell, it's an unresistable penalty for messing with evil high priests, and it's going great roleplaying possibilities. PCs with Curse on them make some very interesting in-play decisions. So Curse is gold as is.
Bless, though, I do kind of miss having having a bless-like effect.
I ended up giving a boon in my DF game - a one-shot use of Luck that the player could choose to activate whenever they wanted to.
It's tempting to allow that as a spell:
You gain the Luck advantage for one use; once used, the spell ends. This does not take an action, it's purely a meta-benefit. This can be lost through your own actions if the GM determines you've been acting evil. Non-good, non-holy, non-believing subjects may cause the spell to automatically fail. At PI 5, you can keep a boon on up to five subjects. At PI 6, you can keep a boon on up to 10 subjects. You can only have one Boon on you at any given time.
Duration: Until activated.
Time to Cast: 20 minutes.
Prerequisites: Power Investiture 5.
I'm not sure I'll allow it, but it's tempting to do so. The "Boon Limits" means you probably can't march in and make a donation and get one cast on you - this is a serious and limited power only for the top-end clerics. Those that have it might be willing to put it on you for a big donation, but then again, maybe they won't - random wandering adventurers without a lot of pull in the church probably won't get it when the local bishop has others more worthy to get it. You could potentially resolve this with the Reaction Roll Table - if you get Very Good or better, the NPC cleric is willing to do it for you. Cost would probably be a sizeable donation - call it $400, like a magic item price - even so, unless you could make a case for it being free and needed (Excellent or better, say).