Spellcasters and Alchemists both have an automatic acquisition method, obtaining additional spells or alchemical formulae as they gain levels.
I assume that it is expected that these will not be the only spells/formulae gained, however, and I wonder what the community uses as a rule of thumb to plan for how many/which spells/formulae you will obtain as you level up.
Do you only make use of the class-granted ones? Do you use a percentage of WBL to "shop" for common ones? Do you just toss in things a few levels below max each time you level up, to simulate discovery while adventuring?