Healing speed has a huge impact on the usefulness of soldiers. A soldier who's "Incredibly quick to heal" will stop bleeding almost instantly and spend a lot less time in the hospital after battles. They'll also pretty much be immune to infection. Not sure if disease resistances affect the chance of getting rotted alive by forgotten beasts and such.
Also, if a dwarf gets infected by a really nasty forgotten beast poison/blood/dust/etc, it's possible for that dwarf's blood to become infected and spread the infection further (and produce miasma if indoors).
The personality if your broker is quite possibly the most important part of the job - you want one that doesn't take breaks or doesn't take time to make decision. I had a broker in a new fort for the first caravan, the broker took a lot of time to make decisions. I had the broker bringing items to the depot, he'd bring an item to the depot, move 40-50 tiles away from the depot with a "No Job" status and then go back to the craftdwarf's workshop that I had built next to the depot and had epic clutter of crafts and mugs, bring 1 item to the depot, move back 40-50 tiles away, move back to the workshop... Needless to say he lost his job once I realized that almost nothing was at the depot by the time the merchants were leaving.