This is an EXCELLENT thread and I 100% share your thoughts.
1) rain collision: I have read recently via another thread that apparently this can't be done. There was a mod that tried to make external houses (where you could go inside but still look out into the real world) but rain still fell in. I think someone called Phitt provided a good explanation on why you can't get rain collision but you'd have to ask him (or if he's reading, perhaps he can explain fully). I DO HOPE though that rain collision will be something achievable because I love to take shelter in the rain and can't stand it when it comes through the roof.
2) paralysis: have you access to the construction set? You CAN make a good paralysis effect with a bow (and one that can send you flying in the air thereby maing an NPC land hard on earth again) IF you have a little scripting knowledge!
If you don't, the best effect to make enemies fall down (drain fatigue is best) and stay down. If you're looking for an effect that makes them fall down a long way, you'd be better off using an enchanted weapon on them to do so, because NPC's are unlikely to just jump off a bridge lol.
I'm sure there must be a way to script it so that after a certain amount of hp damage, you'd be paralysed, but of course hp damage can occur in many ways, and falling off a bridge is one of the rarer ways this would happen (unless you knock them off, which again, would probably be better to enchant an item with either drain fatigue or use the CS to make a paralysis effect).