I'm only redrawing the first 3 episodes of my comic because they were done in a completely different style (fast, cheap, rough) than the rest of the comic (painted, colored, detailed), and I feel they stick out like a sore thumb.
Otherwise the only reason I would go back to redo something is if I made a huge mistake on the drawing, or if a minor detail needed touched up to fit with the plot.
As for my style evolution over the episodes, I'd say I had a "devolution" towards the middle of the comic. I was getting burned out and was too lazy to try and meet the standards I set in earlier episodes. Giving myself more time to complete updates allowed me to put more love into the drawings again.