How can i accurately estimate the strength of this mechanism, and thus deduce the cost it should have?
Do you think this precise mechanism has been suggested before? (note the fundamental difference with the "cloak target thing" mechanism)
Should it be able to hide the colored bars aswell?
Cloak is usually used to prevent targeting. (Because it is hard to hide actual information from veterans) In this manner it is similar to a temporary mass Quint. Your suggestion is better at hiding information.* But does not prevent targeting.
The creature usage is soft anti CC when used on multiple creatures. (Might be better if 1 card can affect multiple targets)
Soft anti CC is balanced based on the additional resources required to succeed with the CC. In general anti-X should cost less than X. So Soft-anti CC should cost less than the additional CC required. Say 1

+ 1 card cost per 3

+ 1 card waste.
The player usage is information denial. (No good comparison to make here. Instead estimate it based on the waste it causes for the opponent.)
No your precise method of obscuring has not been tried before. There have been cards that cloak individual creatures but I think yours is sufficiently different bith in the scope and the type of obscuring.
Yes hide the colored bars
*You cannot obscure elemental quanta from a veteran (

can be obscured but only in character not in quantity). Atk buffs (Overdrive) can only be obscured if used on 1 of 2 or more 0 atk creatures.
How would a SoSa disloyalty penalty be changed to a loyalty bonus? Perhaps lose less hp if mark is
?
Add an optional* sacrifice to heal some of the paid hp. [death trigger]
*See the optional accreation when SoFo turns into a Black Hole.