We happened to mention this QoD to a member of the research staff here, who's a long-time resident of Las Vegas and veteran of the nightlife industry, and she recalled fondly what was affectionately known as the "Soak n' Poke." She remembered -- only hazily -- even visiting the joint on one occasion. She confirmed that it was a notorious party spot, frequented by the great and the not-so-good, "back in the day, when Vegas was fun!"
From our colleague's recollection and what little we could find out online, Spring Fever Private Saunas and Spas comprised 22 private rooms, octagonal in shape, "with floor-to-ceiling mirrors. Lights were dimly lit and very romantic. A small bed on one side, a private sauna off to the other side, and in the middle of the room was a Jacuzzi." It sounds a definite notch-up from your average motel-by-the-hour here, where amenities were/are more likely to comprise one of those vibrating beds and porn channel.
From the odd brief description we came across and the one image we found, taken from a local ad campaign photographed by veteran erotic/portrait/lifestyle photographer R, Scott Hooper, who for awhile was employed by the Las Vegas News Bureau, it seems that it had a Middle Eastern Turkish-harem kind of theme going on, with its blue-and-white mosaic tiling. The ads apparently appeared on billboards, in magazines, and even on TV!
Any facts about the place remain appropriately hazy for an establishment of its nature, which apparently debuted c. 1977 (although some sources think earlier). From a T-shirt we found for sale on eBay, which may have belonged to a member of staff, you can tell there's a definite '70s vibe to the place.
Anyhow, the story goes, as you suggest, that a couple who'd attended Spring Fever were later on vacation in Europe (or Bangkok, depending on which account you read) and were evidently feeling a little frisky, so they apparently visited an adult theater, only to be confronted with a film of themselves at Spring Fever! Our friend and co-worker did not recall any such scandal, however, although she did remember the place burning down, and as Vegas was such a small town then, and she was familiar with many of Soak n' Poke's regular clientele, we're inclined to think that this story may well belong to the realms of urban myth, entertaining though it is. If anyone out there knows more than we do, or recalls visiting Spring Fever, we'd love to hear from you!