Eu tenho que concordar que o texto nas regras originais não é 100% explícito. É claro que você não pode conjurar magias de um nível mais alto do que você tem acesso, mas você pode preparar elas? A FAQ do Pathfinder tem uma resposta mais completa, ênfase minha:
No. You only get the bonus spells if your class level grants you access to those spell levels. You can't even use them for lower-level spells. See page 16, Abilities and Spellcasters section: "In addition to having a high ability score, a spellcaster must be of a high enough class level to be able to cast spells of a given spell level. "
For example, a 1st-level wizard with 18 Intelligence has (according to table 1–3: Ability Modifiers and Bonus Spells) 1 bonus spell at spell levels 1, 2, and 3. However, he can only use the 1st-level bonus spell because as a 1st-level wizard he only has access to 1st-level spells (his class-based number of 2nd- and 3rd-level spells per day are "—", meaning "no access to spells of this level"). As soon as he becomes a 3rd-level wizard, he gains access to his 2nd-level spell slots and can use that bonus 2nd-level spell slot from his high Intelligence, and likewise for 3rd-level spells and bonus spells at wizard level 5.
Basically, ignore the columns for higher-level spells on table 1–3: Ability Modifiers and Bonus Spells until your class grants you access to those spell levels.
A FAQ do Pathfinder é considerada oficial na comunidade Paizo e é vinculante para a Pathfinder Society ( link ).