I'm not sure if snowfall would be appropriate for hoth. In the movies, wasn't the sky clear and blue during the attack?
One thing that I would like to see would be larger smoke effects on burning wreckage. I think that that would add a lot of immersion to the battlefield if you're out in the trenches and three of the five AV turrets are billowing smoke and flame after being destroyed, there are smoking pieces of destroyed snowspeeders, but most importantly, the smoking remains of downed ATATs 