Ropes and rails people, ropes and rails.
I've heard others say it, and I second that if you MUST have an unobstructed view of the parade you have to sit on the curb. Bring a towel. It is, after all, a sidewalk, replete with the detritus of a street. The curb is nearly bullet proof in the "no one in front of me" strategy. However, sitting halfway down Mainstreet the parade can be on you and past in a jiffy.
For maximum band viewing I'd suggest sitting at the entrance hub, facing the castle. The guest band always steps off way before the parade (10-15 mintues - ask a cast member, they'll know). Also, the band will come to the hub and, I believe, take a left, wrapping around in front of the train station before exiting beside the firehouse.
From here you can get a great shot of your band head-on. Flags, majors/ettes and banners included. They will turn in front of you and you can get some closer shots. Partner with another parent on the opposite side of the street (corner in front of the candy store) to get the other side of the band. Finally, make sure there's a picture taker on the train station... it won't be packed yet. We got such good pictures of a band from Pennsylvania several years ago that we printed some and mailed them to the school district. Got a nice note back from the music department.
The ropes, while nearly as good, are seen as open to interpretation by those I refer to as "cake eaters" (along the having/eating lines).
We've had people assume the 12 inches between the front of my knees and an imaginary plumb line from the rope is available. It's not. You can defend this space, but at a cost. If it will upset you to say, "excuse me, this is my space" don't try a rope. You'd think sitting right up under the rope would be a solution, but the four-year old ten feet away WILL eventually grab the rope and treat it like a jungle-gym. You will catch a rope in the forehead.
I love the Pecos Bill's ledge suggestion. It illustrates that you must have Disney helping you out with their rules, not just courtesy.
Enjoy your trip. It will be great!
p.m. For fireworks, curbs don't work. When the show starts people stop in the street and look up. IMO the best spot for fireworks is a spot facing the rail in front of the Plaza or Casey's. Again, use Disney's don't-climb-over-the-fence rule to your advantage.