I checked how much damage my Warriors' Fire Rain and Ghost Blade do and thanks to simple mathematics I'm sure that 1 point at Intelligence gives 10% to damage of a spell (lucky me having item giving +1 to Intelligence). Don't know exacly how those bonuses stacks because when I calculated this way damage which should my spells do with my current Intelligence I got lower dmg by 100%+
one thing for sure: if you're a Mage you don't want to decrease your Int although you're doing some weird challenge
