My experience has been that I have no trouble getting XP for my dragon (on Normal, it's usually several levels ahead of my hero), so I only get the first level of training, and then only because it's a prereq for Anger, which is much more useful.
Definitely max out the Treasure Searcher skill - every extra chest is a boost that makes the game easier. Only summon altars if you want to destroy them (for rage generation). Since the skill only summons damaging altars, I've rarely found them to be more boon than bane in a fight.
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