Great show..be prepared for alittle humidity when you enter the theater, as this is a water show (amazing divers, etc).
No plot to this show, more like a dream sequence, so just lean back and enjoy.
The show is done "in the round", so there really isn't a truly "bad" seat. Although you might want to avoid rows A/B/maybe C as these are in the "splash zone"..no too bad during the hot summer, but you might get a little chilly walking around damp after the show this time of year .
I have been a member of www.goldstar.com since 2006, and have always gotten GREAT seats from them.
You prepay for seats before you arrive in Vegas, but since Goldstar prebooks the theater sections, you always have excellent seats (not the daily "left-overs" like some outlets sell). No hassle, just pick up your tickets about 2 hours before the show...when you pick up your tickets, you can get alittle pickier about exactly which seats you want then.
Rows almost 1/2 way up (F,G,H) are perfect as alot of acrobatics go on over your head - any lower and you might either get wet or end up with a stiff neck from looking straight up.
Full price for Le Reve is around $125-$145, Goldstar is selling tickets for $82.50..but as I said, the seats are GREAT!
You might be able to get cheaper seats at Tix4Tonite or another LV ticket discount outlet, but there are no guarantees...and if there are no discount tickets to be had (shows still sell out, but mostly on weekends), you will be stuck paying full price for not so great seats from the Wynn ticket office....ick! So I play it safe and stick with Goldstar.

I also highly, highly recommend Mystere at Treasure Island...my favorite!
Here is a link for discount seats direct from TI's ticket office..
http://www.treasureisland.com/shows/mystere_by_cirque_du_soleil.aspx
Once again, get seats 1/2 way up for the best view of all that goes on below, above and around you .

Either way, have fun!