Hi Denis,
Just to be clear, a multipler doesn't necessarily add to a game's return. You have to pay for the multipler one way or another--usually, by being required to make a "bonus" bet (one more credit in games like STP; an additional entire bet in UX; etc.)--in some games, a reduction to the paytable. Initially, the game makers/casinos presented these games with both penalties programmed--a larger bet needed to play, with a shitty paytable as well. These games were absolute money vacuums and lost popularity very quickly. So the casinos, for the most part, made the paytables not so horrible. Well, places like SP did, anyway. Strip joints like Sleazars still have the glorious 95% return versions of these games.
Plain old NSUD at SP is breakeven when players' club benefits are considered, which means that whatever promo they'll have going will be a freebie. You also will be rolling the dice on getting room offers in the future, and I mean that gambling analogy literally, because (unlike with almost every other casino), you'll get generous offers if you lose, and no offers at all if you win. But that's South Point's way of doing things. The existence and quality of future room offers may also depend on the nature and duration of the marketing department director's hemorrhoids, which is one possible explanation for their random nature.