My wife and I went to Vegas for my 40th birthday. I was more concerned about eating vegan and eating well (and by well I mean healthily) in Las Vegas this time than I think I was four years ago, the last time we went.
I did get some tips and hints from a couple of on-line veg*n forums. I also stumbled across Surviving as a Vegetarian in Las Vegas.
A couple of places I would definitely recommend, and they both happen to be in the Alladin. One is the Spice Market Buffet. It's one of the best buffets on the stip, especially for vegetarians. They have a Mediterranean station with pita, falafels, hummus, baba ghanoush, dolmas, and tabouli. There was also an Asian station that had a stir-fried vegetables dish, including baby bok choy and lots of broccoli, and a spicy eggplant dish that wasn't really that spicy, though the eggplant was excellently prepared, considering that it's a buffet. Of course, there's always salad, and the American station did have asparagus and mushrooms that were quite nice.
I would also recommend P.F. Chang's. Apparently, this is a chain restaurant. I was not familiar with it before because there is not one in the San Francisco Bay Area that I'm aware of. Anyway... the food is excellent and there are many vegan options. There were nine vegetarian entrees, so plenty to choose from. We ordered the Coconut-Curry Vegetables, the Garlic Snap Peas, and the Vegetarian Ma Po Tofu. We also ordered Chang's Vegetarian Lettuce Wraps and the Vegetable Dumplings for appetizers. Our waiter was excellent (his name was John) and quickly picked up on my being vegetarian. He pointed out that the soy sauce was not vegan because of the sugar, and he brought us brown rice even though we didn't request it. The Lettuce Wraps were my favorite, and the Ma Po Tofu was nice and spicy.
We also ate at the Taqueria Canonita in the Venetian. It has an excellent location at the end of the canal, where the gondoliers turn the gondolas around for the return trip and belt out some Italian song for all the onlookers. We went there because the last time we went they had these excellent tofu tacos. Sadly, the tofu tacos are now gone. Yes, I did complain to the waiter. But I was able to get three tacos filled with mushrooms; it was an option on the menu, and they were quite tasty. But I was still disappointed about not having the tofu tacos.
We had a bad experience with the buffet at Paris. My wife really wanted to go there for breakfast because she heard it was really good. We got up a little late that morning (we had been up till 3 a.m. - but that's another story) and arrived around 10:30. After waiting in line for over half an hour, we were finally seated. Oh, did I mention the jackhammer? They were doing some renovation, and yes, some guy was actually using a jackhammer. Okay, so I was hungry, a little hungover, and irritated by the jackhammer. I wanted to leave but stuck it out because I knew Kelley really wanted to eat there. Because of the renovation there weren't as many seats available; no one wanted to sit too close to all that noise, which you really couldn't escape anywhere in the buffet. So, at 11:00 they begin switching over from breakfast to lunch. Kelley's waiting in line for eggs, which she really wanted, when the guy serving the eggs says that the lady two or three people ahead of her in line would be the last one getting eggs; she was not happy. They had already pulled the oatmeal and the other hot cereal (I don't remember what it was) and replaced them with soups, neither of which was vegetarian. So, a word of caution buffet eaters: pay attention to the times for breakfast and lunch, because they might change it on you while you're waiting in line.
We had breakfast our last day there at the Big Kitchen Buffet at Bally's, where we were staying. It was quite good. I had grits, which I love, and Kelley was able to finally get her eggs. Unlike many of the other buffets we've eaten at, including at the Luxor, Excalibur, Alladin, and Paris, the buffet at Bally's has natural light pouring in from the windows. No, there wasn't really any view to speak of, but it was pleasant to eat in natural light, while the other buffets are all enclosed or underground. And the food and service was good.