So okay I have this instinctive thing and never make a mistake casting my simpler spells. What about when someone's swinging a sword at my head, I can still do it then? The rules say the cast is at -2 but it doesn't matter because I never fail. What about if I've fallen off a cliff and I'm plummeting to my death? That's serious pressure, must be worth at least a -4 penalty but of course it doesn't matter because I never fail. What about if a demon is pulling my entrails out through my chest? Okay it's getting silly, but the point is a big bonus or penalty is always better than automatic success or failure.
Then there's the inconsistency it causes with Minor Magic. You have no chance of failure casting 1 point spells but can still fail with the even simpler Cantrips? That seems to be what it says. But if you instead extend the no fail to Cantrips they never cost MP to cast, which also isn't great.
So the case against the accused was building anyway. But the kicker for me was noticing what happens with Natural Mage and a Sorcerer. A Wizard with 5 in the Special Skill automatically succeeds with 1, 2 and 4 point spells but still has to roll for 6 and 8 point spells. But with Sorcerers their spells all cost less than 5 STAMINA with the exception of ZED! So that's not fitting "the less demanding spells in their repertoire" description very well, although personally I don't think 4 point Wizard spells like Lightning Blast fit it either.
So this is my suggestion:
Simple as that. It only affects the easier spells and gives a competent mage almost automatic success as long as they're not trying it in difficult circumstances. If +4 isn't enough for you it could be +5 or even +6 like Cantrips. 1 and 2 MP Wizard spells make up roughly the same proportion of all the spells available to them as 1 STAMINA spells do for Sorcerers so it's even there too.Natural Mage
A Hero must have at least one point in the Magic-Wizardry or Magic-Sorcery Special Skill in order to choose this Talent. If chosen, the Hero has an instinctive understanding of the less demanding spells in their repertoire. The Hero has a +4 bonus to the spellcasting roll for all 1 and 2 MP Wizardry spells or 1 STAMINA point Sorcery spells.
As a side note I'd also change the Focus Talent to a +2 casting bonus. At +1 Focus was seriously underpowered compared to the old Natural Mage. But with Focus being +2 for all spells and Natural Mage at +4 but only for the simpler ones, the two balance against each other nicely.