There are powerful Blood abilities out there, some of them are quite useful in many situations, others are overpowering and yet others are next to worthless, it all depends on the situation the scion is in at any given moment. lets for example take an adventuring based campeign (as opposed to political) and a mighty 15th level fighter scion who has the Blood ability Major Resistance: Non-magical attacks at either major or great Deriviation. now this ability grants you as you should be familiar with Damage Reduction either (major) 3/+1 or (great) 5/+1. Most opponents that the Scion is encountering at that level (since he is probably traveling with charecter at ECL 16/17) either have damage reduction that enables them to easily bypass this damage reduction or they are armed with weapons that enable them to bypass this ability rather easily.

The great blood ability would be alot more useful and understandable if it were something like what I suggest is that the Damage reduction increases as the charecter does in level great Resistance for example might gain one point of damage reduction per level(ECL/level?) also that the plus of the magical weapon required to injure the scion might increase as well at every five levels or in the case of the fighter scion above he would have Damage reduction 15/+3

The Major blood ability would then be something like this 1point of damage reduction per 2 levels and the plus of the weapon requered to injure the scion might increase every 7 levels (in both cases rounded down)
or incase of the fighter above he would have damage reduction 7/+2

also to make sure that they are not completly useless for a first level scion there should be bare minimum of the damage reductions as they are or in case of (major) this should be DR 3/+1 and for great this should be 6/+1

there are more abilities out there that could use revisement on this count, for example animal affinity(great) grants the scion the ability to change into Totem animal once per day(this should change to be once every 5 levels of the scion)

Blood abilities should be useful at all levels, not the just the lowest or the highest, feel free to tune down some abilites and then gradually increase the power level of them, some blood abilites are equally useful at all levels for example Long Life ability and should not be changed