I think I'll just give a +1 to AC at 5, 10, 15, 20, 25, 30..
Also, rather than making masterwork weapons, I may just reduce monster defenses by 1/tier. (As was suggested by garthanos in this thread: http://www.enworld.org/forum/d-d-4th-edition-rules/259514-disarm-d-d-4th-edition-4.html )