Unfortunately, func_models are treated like any other entity, so, while they usually draw faster, they add bandwidth (so having a huge number of them is a bad idea). They are also vis'd based on a single point, which is why tree models sometimes disappear if you can't see the base of them.
You could probably pull it off using big groups of icicles, and only having 5-10 visible at once. Ultimately, this is the type of thing where we really need a new map format...
Some day... maybe...