I went to Las Vegas for three days almost exactly five years ago and that was more than long enough. It was too big and loud for me. There are some great things to do there, and I am glad that I went, but was also glad to leave - especially since I went to San Fransisco next and loved it there
It was great to see some of the shows and the sheer scale of the hotels, and the lights at Freemont Street. Also we flew to the Grand Canyon from there, which was amazing

but if you aren't really into gambling, which we weren't, it gets too much after a while, as the noise and lights never stop. Also, because the hotels were so big, it took a very long time to walk anywhere.
I think that it is a great place to visit, but I think that you need to combine it with somewhere else.
Nicola