I seems a little odd to me that specialist wizards should be able to cast spells from their opposition schools from spell trigger or spell completion items without any penalty. Given enough downtime, a wizard with say, Evocation as an opposed school will be able to create say a Wand of Fireballs, and basically ignore the penalty on casting spells from his opposed schools.
To counter this, I'm proposing a simple set of house rules:
1. When casting a spell from an opposition school using a scroll, a specialist wizard must have double the minimum caster level of the spell to automatically cast the spell. Otherwise, he must roll to avoid a mishap as per the rules.
2. When casting a spell from an opposition school using a spell trigger item, such as a wand or staff, the specialist wizard must expend double the listed number of charges.
3. When creating an item containing one or more spells from opposition schools, the cost of making the item is 50% more than the listed price (with creation times increasing accordingly).
This hasn't been play tested, and some tweaking may be necessary, especially for rule 3. But it limits specialists in what I feel to be a logical fashion, one which is consistent with the new rules. And it's still a better deal than specialist wizards got in 3.5.
Thoughts?