The chance to hit / be hit will change in any case. These values are calculated based on your current stats, so increasing agility will increase your chance to hit and decrease your chance to be hit. Part of these values are based on your luck, so there is a small random component you can observe by opening and closing the trophy list multiple times.
My strategy focuses almost exclusively on sharp and pointy objects, so I have not really been paying too much attention to resistances, besides checking the main characters' resistances in different difficulty settings. In the beginning of act one I sometimes switched between crushing and slashing weapons, but late in act one I changed my hero to a crossbow pretty much full time. With the hero doing crushing and piercing damage and the DK doing slashing, I don't run into too many opponents I have to even consider resistances for.
