No and yes.
No because the structures add in a large creative and innovative component to a given display and make it technically more appealing in addition to providing it to become much more integral in its entirety, particularly when they enforce a theme gracefully.
Yes merely because I feel extra structures have a tendency to make those particular displays that employ them to sort of give a natural advantage over other competitors that don't make use of these at all, especially considering that not every display involves them. Of course, this argument is nullified assuming that every participant uses structures, and the fact that they don't secure a spot for a team to be on the podium just because they used them!
For the most part, I find the extra structures very effective depending on how any given team uses them, just so long as they are relevant and consistent with the thematic framework and are at least at times active with whatever fireworks are exploding around them, as what was seen with the towers and arcs during the American performance. I found the Portuguese ring from 2002 used pretty well (as was the pyrodome in 2005), and of course the English ring of last year (2007), just to name a few.
Overall, though, I would be content either way, clearly seeing that many participants operate very successfully without them anyway - there's multiple ways to exploit creativity, and it doesn't necessarily only have to be with structures, lasers, etc. - they are just one effective method to bring out creativity and/or originality more sufficiently.
Trav.
