Ah, I wasn't sure if you happened to live up there too.
I saw a person being pooped on once. I was standing at a sidewalk cafe, underneath an underpass, and a couple was walking down the sidewalk talking. The woman stopped and suddenly let out a shriek.

We all stared at her. She didn't look like she was having a mental breakdown. Then she pointed to the poop on the side of her head.

Luckily, being at a cafe, they had plenty of napkins for her. It always makes me look up before I'm walking under an underpass now for kamikaze bomber pigeons.
Yes, that would work too. Just remember, you may need to get tickets days ahead for the Top of the Rock or the Empire State Building. You don't want to have to rush or cut your time at one of the other sites short to get there for your chosen time slot if you plan it for later. And you may have to stand in line, (even with a reservation) possibly several minutes(?) early? The times I've walked by, there have been lines waiting for the elevators to open, so they get in right away. If they have no shows, they might have a wait list to fill in, which may be why they want people there early. But, I'm not sure. I haven't gone in many years.
You may also want to have alternate indoor plans too. The Museum is fine in any weather. (Again, may be busier if it rains.) The other three events are outdoors.
The Empire State Building, I think, has an indoor observation deck. Yet, if it rains and the clouds are low, you may only see a gray cloud all around. Similar for the Top of the Rock. You might not get to see the top of the Empire State Building, just know it's behind that gray cloud ahead. (You'll be able to see the bottom part.) While NYC is beautiful in any weather. Your view of many other sites may be obscured: the Chrysler Building's art deco spire, One World Trade building, and way off in the distance the Statue of Liberty may be blotted out.
The SI ferry schedule may run slower in the rain, which affects your time to do other things.