I'll answer your questions from an informed point of view being that I've owned and operated a rig for a few years:
can you run them over a crowd?
Definitely not a dense concert crowd. Lightly packed and from a safe vantage point, yeah. You can. You can get a really nice complex crane shot all with a piece of equipment that can be carried in a small pelican.
Can you run them inside?
Again, pick your situation wisely but yes with the Solo and the Phantom 3 it's becoming much more practical to do so.
Can you run them over water ?
Yes. All day, all night. If something happens over water it would not be anymore devastating to the craft than if something happened over concrete from 30 feet in the air.
Can you run them at events? in public? The short answer is yes.
For real estate there's always google earth.
People wouldn't be asking for them and paying for them if they wanted to show off their real estate using satellites.
Just saying. Also, less unnecessary spaces in your chicken scratch brah.
Damn, I would LOVE to travel to Africa and film poor people! These days that actually DOES qualify as doing something. People don't make it beyond their neighborhood when making "documentaries" on their DSLRs.
I've used the GoPro Hero 4 Black extensively with my aerial rig as soon as it was released. So I have first hand experience to see that higher frame rates only reduce the quality of the image. I will occasionally use the 2.7K/48FPS option if slow motion is really going to add to the action, but the 1080/120FPS looks like garbage. So I have no interest in even going up to 2.7K/60.
Noam Kroll explains why in his post about the GH4 and avoiding 96FPS
I don't mean to shit on your point / choice, but I just had a 6TB version of one of those die on me. It's about 4 years old so maybe that's it's life span. Everyone should definitely be thinking about re-backing up your data around the 3 year mark.
I'd rather GoPro introduce a higher higher quality camera than what they plan to do with the Hero4. Something that has decent dynamic range and records to a codec that's not compressed into garbage.