Nope, you're the first. We've answered all kinds of visitor-profile queries in the past, not to mention specific QoDs about where to attend midnight mass during the holidays, or how church collection plates handle donations proffered in casino chips, and even where the nearest Alcoholics Anonymous meetings are in relation to the Strip, but your query is the first we've received concerning how many visitors attend a religious service while in town. Still, inspired by the comments of a Yelper we read, who observed that "Hanging out with God during a trip to Vegas seems like an obvious necessity, regardless of whether or not you are gambling," we figured we'd look into this.
It turns out that it's is not a statistic tracked by the Las Vegas Convention & Visitors Authority, nor by any other "official" source that we've located to date, so for the time being we're left to extrapolate some sense of the answer to your question from various anecdotal sources.
A great resource turned out to be a 2014 feature by the Las Vegas Review-Journal's John Przybys, titled "Local houses of worship work to welcome visitors from around the world." For the piece, the columnist spoke with a number of religious figures around town, including an Episcopalian usher, a rabbi, and both Mormon and Catholic bishops, all of whom had some interesting insights to share when it comes to out-of-town attendees at their various houses of worship. We recommend to you the entire article, but here are some highlights:
Indeed. We note that the Shrine of the Holy Redeemer has a 4.5-star rating on Yelp, resulting from 22 reviews, the majority of which are from tourists. Here are some examples:
Bishop Pepe made some interesting observations, including the fact that, this being Sin City, it's not unusual for a visitor to reach out for spiritual guidance and support, more so than might occur in any other typical tourist destination. "That happens when people get into trouble in town," concurs Rabbi Harlig. "It can be financial trouble. Sometimes it's religious. Maybe they’ve done something inappropriate." He observes how at times it's more comfortable for someone to confess to or seek help from someone who is not their community rabbi and who doesn't know their family or social circle and will likely never see them again. No doubt the same holds true across all faiths.
We'll conclude with a telling excerpt we came across on the website of the 7th Day Adventist Mountain View Church (6001 W. Oakey Blvd.), which states: "We are happy to have out-of-town guests at Mountain View Church. We are always enriched when we are joined in worship by those who wish to spend the Sabbath among believers. Las Vegas is a city that brings lots and lots of guests who wish to visit our area. Guests in our area either visit as tourists, attend conventions, conduct business of one sort or another, or connect with friends or family" and they're happy if you choose to include them in your plans. However, this church also felt compelled to explain that, due to the high volume of requests received and time restraints, the church cannot pick you up from or deliver you to the airport, nor can they take you on tours of the area, nor drive you to/from Sabbath or other services and wherever you may be staying. We figure only in Vegas would anyone even expect that they might!