have seen both Vegas & Downtown Disney Cirque...we enjoyed both shows very much. Saw Vegas show in June 2011, and saw Disney Cirque in February 2012.
The big difference was the price...the Vegas show we were able to get discounted seats (direct from Cirque Soleil...they had a 50% off sale going on their own website because it was Vegas off-season...June) Think we paid in the range of $50 a seat.
The Downtown Disney Cirque does not seem to do any price discounting, so it can cost more that VEgas. I think our Disney Cirque seats were more like $90 However, you do not have to buy the "best seats" to get a good view, either place.
Was the DTD Cirque worth it? Yes, I think so. WE did not buy front-and-center. We actually bought 2nd (or maybe 3rd?) price-tier seats. Our seats were way to the left - about as far to the left as you can go, but just a few rows up from the stage level. We had similar seat in VEgas so we knew that there would be only a very few things going on that would be harder to see, but the majority of the show was easily viewed from that area. The fact is, the Cirque shows have stuff going on all over the place (above you, to the left, to the right, directly in front, in the air, even in the audience sometimes) There's so much going on, you're going to be entertained no matter what.
I think the only place where you would really have a very obstructed view would be the very top rows if your were extreme left or right.