Is it worth going while raining?

I wouldn't recommend

I wouldn't

I wouldn't enjoy it as much on a rainy day

Depends on how wet you want to get. Almost every exhibit is outside.

I would say no.

I wouldn't recommend going on a rainy day.

It really depends on how much and for how long. I would recommend going if it is just on and off drizzling. If rain is forecasted all day I would say no.

Well some areas you'll get wet but most areas are well sheltered. I wouldn't go on a rainy day though just because I'd want to spend time observing all the animals.