I also dont see trauma as giving a penalty to attacks. If anything, 4th Edition seems to suggest that creatures often capitilize on being bloodied (via immediates and reactions) and it would probably be unfitting to tack on a penalty right after a creature used that ability. This is in no way about reality or any other -ism, just about theme. Additionally, weeks of rest could severely rape the flow of a good dnd session, unless they were specifically accounted for. As an adult gamer, our sessions are limited due to spouse, work, and family priorities, and we have to make the best of our time.
On the other hand, I do like the concept of fights leaving their marks on the characters. Maybe it should somehow tie more to healing surges (as suggested above) or longer rests (of both sorts). Players despise penalties, and usually conveniently forget them, leaving the responsibility for their implementation souly on our shoulders.
In other words, though not well-stated, I think it depends on your particular fellowship of players.