I used to get a super ability from the dwarves. True, in the campaign in the expansion pack, right before the very last battle, I completely sacrificed my luck. I think even in a normal hot-seat game, it's better to improve luck, because it's harder to play without it. Also, improve the ballista and defense.
2 silovik - it depends on how long the battle will be. Because if there's a chance to quickly defeat the dwarven creatures, why expose yourself at the beginning of the battle and go to the ballista? If you have powerful spells, then there are no questions!
Here's a screenshot of the moment I received the super ability from the dwarf in the campaign.