Sorcerers should be placeable on a portal to reduce either the amount of corruption you get from using it, or reducing the amount of time it takes to cleanse the tainted penalty.
T4 thralls should also give more blood when sacrificed, maybe 2 or 3 instead of 1.
I like your first suggestion. Sorcerer thralls have too few uses. (In fact, they have no real uses, but at least I’d like to place the enthralled once to workstations.)
The second suggestion, even though I understand that using a T4 as a sacrifice feels like you’re sacrificing something more than just a dude, the fact is that there’s only so much blood in a human body, and that amount doesn’t increase because the person is famous.