Originally Posted by mbstone
Buy a massage (or other spa service) and they will throw in admission to the spa for the rest of the day.
This is a tried and true method. My friend (a dude) just got a manicure at the Wynn while his wife was getting a facial. He service cost $35 and it was $30 to enter the gym normally.
The other option is to ask if the hotels offer a multiple day discount. You can usually save a couple of bucks by paying for three straight days at a per-day discount (ie. $60 for three days or $25 each day)