Regarding the actual "opening" of a casino, most open on a Thursday at exactly midnight, and generally throngs of people wait in line for up to half a day to say they were the first to get in. Most locals I know are equally curious, but wait until Monday or Tuesday to go see the newest casino - after the weekend tourists leave town.
(FYI - most casinos open two or three days prior to the official opening just for the employees and their families - they all get free rooms, "fake money" to play and comps to the buffet and restaurants and see the shows - this is to make sure everything is up and ready for the "real" customers.)
I have been to the openings of Paris, Mandalay Bay, Wynn and The Venetian...the worst of which was The Venetian; they opened a full two or three weeks before they should have. Hardly any restaurants were open and much of what you can see today was still under construction. The others ran like clockwork.
Personally, I wouldn't want to stay at a hotel/casino on opening weekend - the casinos are busy enough on weekends, but you can't begin to imagine the throngs of looky-loos marching through just to say they were there. Every slot machine has someone sitting there, every table game is full, every restaurant has a line and you have to wait for everything. Granted, it is fun to say you were the first and report back to friends and family - but it will be anything but a stress-free vacation. If I were to stay overnight - I would come mid-week, the first week, and plan on going down to the main casino floor and checking things out at odd hours - early in the morning or late, late in the evening. The crowds will be thinner and the lines shorter and, without the masses that look like a moving mosh pit, you might even get a glimpse of the carpet - which may or may not be a good thing. Las Vegas casino carpets are designed to make you want to look up again quickly.
Still, should you go to any of the next openings - be sure to write back and give you first impressions - that is, after all, one of the main reasons to put up with the hoopla.