It's not just that they are not rewarding, it is a waste of time trying to find one to do. Why travel around aimlessly, trying to find an active one, only to have it completed before you arrive, and be forced to do it again. At least with the dragons you can tell on your map where you have to travel. This whole "random" harrowstorms is poorly designed. At least the dragons rewarded you with a furnishing plan every so often.
I've noticed that since the patch people are less likely to call out which hs is active in the zone chat. Probably because no one is doing more than one now.
But the yeah, the rewards are not worth the armour damage of trying to do one without a horde of other players. And for soloing they're too much of a pain, what with the regeneration and world class bosses spawning if you're not fast enough.