when are stats more important than att?

Att does more for non-magician characters than ma att does for magicians. At the higher lvls as I recall 7 stat points = 1 att. So, a 3 att cape will be the equivalent of a 21 stat cape. For magicians, as Cyanne pointed out, int is more important than ma att, but that's because every 10 points of int give you more MP during a lvl up, and int is affected by Maple Warrior. However, in terms of direct calculation of attack value, 1 int = 1 ma att. Because of that, in FM people will be advertising for something like a "114 stat Maple Shine wand," which might be something like 101 ma att, 13 intelligence. An 9 ma att, 4 int purple cape is equivalent to a 13 int yellow cape, (but worse during lvl ups,) but a 4 att 2 dex cape is still very good despite the crappy scrolling job.

Hope this helped.