When assigning to dead monsters you could cross out (X) an unused square for that monsters power of Hp. Will not count as victory point.
Further more when there are no spaces to cross you must cross into another monster of your choosing.
Will give a visual indication of an action you performed.
Will limit the number of times you can assign a die to a dead monster. Making the game a little more difficult.
Will not allow you to kill a full monster only to have it used as a recycle bin later.
Same with Treasures.
I like this idea and will be trying something like it with the next adventure. If it works I may look at changing the main rules to reflect this.