Is the attic temperature- and humidity-controlled? If not, the heat and humidity that can form in attics might cause repairable problems with the discs, such as warping or data layer adhesive drying out and separating.
Ditto for all things electronics, especially if they are not wrapped in plastic with a silica gel packet to absorb water (and those can only absorb so much moisture over time as well.)
Our attic isn't technically "finished" but it it's a real small house and the roof is insulated so it doesn't get very different (climate-wise) from the rest of the house. But, all my stored DVDs are in sealed plastic tubs so they are fairly well protected.
Thanks for the advice though!
--Alex