Here is the information on the workout room at WL. My wife and I were just there and worked out every day. The rates are: $15 / day; $25 / person, length of stay; $45 / family length of stay. (We chose the latter. They write "FLOS" on your room key, which you bring with you daily.)
The weightroom was pretty good, and was most crowded between 6.30 and 8.00. (Most people were like us--they worked out before going to the parks.) I asked the young man who worked there and he said few people came in between 9.00 and 5.00. The room is open from 6.00 am to 9 pm.
There is a bathroom, but unless I missed something, there was no shower. Also, the bathroom is actually outside the workout room, so if you leave to go the bathroom, you have to go all the way around to the front of the villas to get back in. This suggests that they do not see the facility as something that exercisers will use, and thus my hunch is that there is not a shower.
The machines are good, with a full Cybex circuit, a number of dumbbells and an area to bench and squat. The free weights area is small, though, so more than three people gets crowded. There are about three exercise bikes, treadmills, and elliptical machines (9 total). All in all, if you like to work out, they should have what you need.