What this does is push conviction up the totem pole of wizard skills, so that choosing your pinnacle wizard skills is harder. Also, you want all three as high as possible, which is one of the real weaknesses of wizards: they usually want three pinnacle skills (Discipline, Lore, Conviction) that have sort limited utility in other situations. Then, if you want to be a fighting wizard, you have to squeeze in athletics and alertness and ... But, with the removal of block power being based on your conviction, a wizard really only 'needs' a conviction of 3 for the 4 mental stress boxes. That leaves him more skill options than a stock wizard.
Hmm... I would agree with your description of how Wizards currently choose their skills. I'm not convinced that having three pinnacle skills is an absolute requirement for Wizards to be interesting.
Consider this: Under the current rules, it is difficult to create a High Conviction, Low Discipline Wizard. That character has access to big shifts of power, but can't control it without spending Fate points or tagging Aspects. So most of the time they would have to settle for weaker spells. The Houseruled Wizard could pull off a High Conviction, Low Discipline Wizard a bit better, since screwing up a spell would earn them a Fate point (which they could use on future spells).
I guess my point is, while I acknowledge that these rules would change the baseline for what skill levels a Wizard needs, I don't see why that is necessarily a bad thing (or a good thing, really... I see it as a neutral thing). From an optimization standpoint, Discipline is more important than Conviction, but so what?
And, of course, a Wizard with Conviction 5 could blow up two zones in one exchange, rather than just one, which is kind of cool.
Anyway, let me ask some practical questions:
1) Would it help if there were more options for "Spell Power"? Currently, we have two options (Reduce Power by 2/zone, Reduce Power by 2/exchange). What about adding more options?
- Reduce Power by 3 to add a Maneuver
- Reduce Power by 2 to move the target one zone
2) Would it help if we used Spell Power (Conviction + Specialization) to add duration to a Block?
- Evocation Blocks last Spell Power/2 exchanges
Both of those options might make extra Conviction more interesting. What do you think?