I think a Commercial, and Experimental are all that is needed. Amateur could be put into Experimental since they are usually garage built hobby planes.
I think weight, noise, and engine type for subsections. Turbines are loud I wouldn't want them buzzing the neighborhood skies.
Another further subsection could be "sensor package".
Do we really want video cameras and thermal imaging sensors hovering over our backyard taking pictures? I don't. If it's just taking the temperature I wouldn't care, but if it's taking pictures that's a little more intrusive. So sensor types is a definite category imo.
That's up for debate.
Try taking a picture of a hot woman tanning naked in their backyard from a drone and posting it on the internet.
It might not be illegal but it's something that will get the attention of the public real quick.
The American people are going to demand for "reasonable privacy" when it comes to drones. Especially one's operating at such low altitudes as 400 feet.
For example I think it's already illegal to photograph someone on private property and distributing it.
The main problem is that the public doesn't realize that they really have no privacy in the first place. Then we get ignorant citizens hollering about how certain technologies will take away their privacy.
Anyone can take pictures all they want. Your only legal expectation of privacy is in your home, and only then after you've take reasonable steps to ensure your privacy. No fence + no curtains = no right to privacy.
What people don't seem to realize is that you have virtually no right to privacy from other citizens, and only a tiny bit more rights against your government.
All the UAV revolution is doing is bringing down the cost of what is already legal spying. Therefore it is totally inappropriate to try to regulate UAVs for this reason. If you want more privacy rights then petition for stronger privacy laws, we should really have a hell of a lot more privacy than we currently do and I'd support you. But banning or over-regulating tools based on the possibility of what they could do is completely wrong.