It's hard to get comped at a hotel the first time you're there unless your just throwing money around carelessly and they see an opportunity to milk you dry. And sports betting is really tough as there such a limited cash turnover compared to betting a $100 a hand at blackjack or craps.
Most of the hotels have raised their minimums and limits as to who gets comped, but I'll tell you this, if you don't have to stay on the strip, Station's Casino's like Green Valley Ranch and Red Rock are pretty aggressive in customer appreciation. The other Station's Casino's are dumps, but those two are stellar 5 star.
But I wouldn't gamble just to get a nice room. If you're a modest bettor, it might be cheaper to just pay for the room you want, then use your player's card to rack up points for the next trip. Vegas has gotten very stingy in recent years. Even the Golden Nugget is hard to get comped - go figure!