I can suggest a few things to go along with what One-Eyed Jack said in the newsletter. What I mention for Bumbaloons goes for Buffaloons too.
Don't immediately attack. Group you and your Companions so that your long range fighters are protected as much as possible (preferably there are only one or two squares that they can be attacked from). Use buffs to help your group achieve maximum damage/protection. With the changes, use the 10 turn buffs first and, only when the Bumbaloons are close, do you use the 3 turn buffs. That way your group gets the maximum use of the 3 turn buffs. Use the AOE (area of effect) attacks when you can do the most damage to the most Bumbaloons. Attack the same Bumbaloon, unless you are sure you can defeat it that turn and then attack the next one.
If my health is below 80% of max (if max is 100 and I am 79) and before I fight them, I would take time out to replenish my health at a Life Fountain. Sure, it takes more time but usually I am able to defeat the Bumbaloons without being defeated myself.
Try to make sure that you have all the Bumbaloon or Buffaloon quests at one time. This means you only have to fight them once instead of several times.