just as a disclaimer, i have never seen anyone use or even learn erase. having said that....
since the spells says, "up to two pages", it infers that the amount of writing erased can be controled. but, there are rolls associated with the erasing, so i would say:
'nonmagical writing automatically erased if you touch them' (as per the spell, even specific lines)
"Otherwise, the chance is 90%." ( i would lower this to note the precision of the spellcasting, based on the situation, as much as 20%)
"magic writing must be touched, and you must roll 15+ on a caster level check" (i would raise this to 20+ and/or raise the miss chance from a natural 1 or 2 to 1 thru 4)
just some thoughts....