I didn't realize that OKW did massages (though I think you can get in room with prior arrangements). We did Grand Floridian one trip. It was nice but not great depending what you/she are use to. It was also more pricey than the day spa near my house (which is in the top 20 in the country) and lacked a lot of the spa atmosphere.
Sorry, I can't give you more info on Institute, I've never been there. I guess the bottom line is, I have now opted out of this service at Disney. I figure it isn't worth the time/money considering everything else there and the services near me.
Good Luck!
Sandy