In a game where my Wizard hasn't been able to pad his spellbook, he's had to rely on what he gets. Still, Wizard spells are often versatile enough that he doesn't need to know more than his 4 spells per spell level, though having 10 spells per level sould be very handy.
In another game, the Wizard got spellbooks filled with free secret page spells and it didn't upset the game's balance since the used a small number of spells anyway, perhaps 5 per spell level.
