I'm another one who will always add a little Blood to any game I play. Even if it's thematically inappropriate ... Ulm Reborn, for example. A little bit of Blood can open up a lot of possibilities.
Succubus.
Infernal Disease.
And my favorite global, The Looming Hell.
Blood forging (as others have said) is probably the best way to get some mileage out of a little bit of Blood, because
it doesn't require you to spend any research effort on Blood magic. All you have to research is Construction -- which you're going to research anyway -- and you can get some very nice possibilities:
- Lifelong Protection
- Soul Contract
- Armour of Souls
- Blood Thorn
- Blood Stone
- Boots of Youth
- assorted artifacts!
A little bit of Blood can go a long way. I think it's well worth the marginal effort required.