Hi Shan -
DH and I both had one there a few weeks ago. I'd suggest making an appt ahead of arrival...it filled up pretty quickly while we were there. You can schedule it so that one of you is having the massage while the kids are at the unbirthday party...worked well for us.
I don't remember a discount...but we didn't wait til Wednesday...I wanted to relax early. I had the traditional swedish (65, I think...maybe 75) and hubby had the deep tissue (around $10 more than the traditional)...we both thought it was grrrrrrrrreat! When I've gone to the spa for a massage a 20% tip was suggested...that's typically what we do.