My sister did this with her Husband and I was a bridesmaid.
Then 2 years later, my friend and her Husband did it.. and I tagged along as the photographer! It was just us 3 and we had an awesome time (they're not coupley and we've been on holidays before as a 3 .)
My sister got married at the MGM Grand as part of a Virgin package deal. We also stayed at the MGM Grand.
My friend got married at the Little white chapel, the same place Britney Spears got married - They stayed in Paris.
I think it worked really well for both couples as you have much less pressure and the day is whatever you make it - In both cases, the brides had their hair and makeup done, my sister got additional baggage allowance for her dress and we all stayed in the Virgin Lounge before we flew which made things a bit nicer!
We did a Limo tour of all the casinos and did loads of other fun things, so it was a total holiday. Despite Vegas being primarily for gambling, I think we spent an hour or so playing roulette and the rest of the entire time in Vegas doing other stuff - Watching shows, shopping, going to see all the animals (Flamingos in the Flamingo hotel, Lions in the MGM etc).
All the friends and family could watch at home as it was live on TV... and despite the registrars doing hundreds of weddings each week, they appreciated every wedding is special to the couple so it didn't feel as if you were just 'one of many' getting married.