I didn't notice needing to repair the dragonheart armour more frequently than other breastplates, despite the low durability. As you say, that can be a problem with weapons, though.
Hearing bonuses let you hear opponents from farther away, and can at least give you a bit of advanced warning of what opponents are ahead. I found hearing in general to be occasionally useful, but wouldn't necessarily pick a hearing bonus over other options if given a choice.
Sight bonuses (either from equipment or the Elven Sight / Ranger Sight skills) determine how much fog of war you clear as you explore. I boosted Elven Sight (which is much more effective than Ranger Sight) until my sight range got up to about the screen size and then started avoiding equipment with sight bonuses (so I could use the fog of war to keep track of where I had explored).
sights and weapon rangeMost spells that can be found on weapons are similar to the corresponding spells you can learn. Frost(4) is similar to level 4 of the Freeze spell, with the notable exception that Frost on a weapon ignores the target's resistance, so always works.