Personally, I like the idea of giving armor a DR rating that can bypassed by a high attack roll, but I'm thinking about handling it a little differently.
First, I'd replace the existing armor types by dividing them up into DR levels (representing material types) and coverage ratings (representing how much of the wearer is actually covered by that material), which would be the amount by which an attack would have to exceed the wearer's touch AC in order to ignore DR. So a breastplate would have a high DR, but a low coverage rating, while a full suit of leather would have a low DR, but a high coverage rating. I've been thinking about having DR range from 1 (leather) to 5 (plate), and three coverage ratings: 5 (chest only), 10 (partial body), and 15 (full body), but I really don't know about the balance implications of these numbers.