Buffing any particular avatar is nice, I guess, but the Troll/Unicorn bells and whistles are not useful to a wizard who expects to fight. Wizards fight with the killing curse.

True, but being hit with AK isn't the only thing that can disembody him. Other magical attacks, dangerous magical creatures, muggle attacks, magical or mundane accidents, etc., would not be a threat to him with Hermione's new protections. Being disembodied would be a serious setback for his current plans, and would leave his horcruxes vulnerable until he could find a new host, so I think it's reasonable to want to take precautions against stupid little unexpected things that could cause that.