Well, did some more testing last night to see if elementing on your bow helps with aoe damage. I tested on Captain Carrierbombs as they were handy and I was looking for a mob neutral to both fire and ice.

These images are an example of the average damage difference between the two bows. It’s not a single example of each with 1 high and 1 low damage. I understand than there are small differences between identical attacks so these are what I would consider the "average" damage of each skill with different equipment on the same mob.

I started out with 2 +8 Guardian bows, one clean, one with +6 fire I bought in a shop the other day.

Ice Arrow

First, clean bow using Ice arrow.


Now +6 fire elemented bow.

As you can see it adds about 20 dmg. Not hardly worth it but every little bit helps.

Flame Arrow

Clean bow

+6 Fire bow

Now you’re talking! Adds around 60 damage to the burn, not sure what the initial damage difference is but probably near the same.

Arrow Rain

Clean bow

+6 Fire bow

Similar to Ice, only adds about 30 dmg, but times 4 hits that’s still a fair amount.

Piercing Arrow

Clean bow


+6 Fire

Finally, piercing arrow again adds around 20 damage.

Conclusion

As you can see it helps. Not a ton but it does make a difference.
I’ve not tested it with any other elements but I’ve heard none of the other elements help.

Credits go to power_one.