I'm re-reading the core rules at the moment, preparing for a BR campaign ... I'm still a little unhappy with the notion of dealing with up to six or even eight rolls if someone whants to try arcana like "Mind Delving" on an unwilling subject (opposed rolls for establishing psychic contact, for not being noticed, to overcome a psychic shield, than an opposed roll for Mind Delving ...).
I was toying with the idea of, instead of Opposed Rules, just using a "Mental Defense" of 10+Willpower (Self-Discipline) to be rolled against; I'd make Psychic Shield an exception, though, in that it allows to make an opposed roll.
I'd also stick to one "attack roll" for a spell that stands against all resistances and opposed rolls.
So, if you wan't to secretly establish Psychic contact with an unwilling target protected by a Psychic Shield, you'd make a roll against 7+familiarity. If you're succesful, you'd compare that to the Targets Mental Defense; if you match or exceed that, the target gets to make an opposed Psychic Shield roll against your Initial roll. And since you want to do it secretly, the target also gets a Perception roll against that same number.
That way, establishing psychic contact involves a maximum of three rolls, not six. After that, you're ready for the actual arcanum that you mean to use ...
Also, I'd extend the rule that only active rolls (not resisting rolls) can generate stunt points and rule that also, you only get to generate stunt points once per action (i think I actually woudln't Need that rule with my house-rule that the initial arcana roll stands, but still ...).