We sat in the center of the front section (Row F one year, Row G the other), and really had no problem viewing anything. It's true you have to look up for a few of the acts, but I love sitting that close for the intimacy of it. The stage is just "right there" and you can really see the performers faces. It makes it easier to become absorbed in the performance (for me, anyway).
I always wear something nice to Cirque. Nothing fancy; just a nice pair of pants or a skirt and a sweater. I believe strongly that you should dress for the theater, even if you are at Disney World! But, having said that, I have seen people wear very casual things, looking like they just came from the parks.
Have a great time! La Nouba is absolutely wonderful!