I purchased leather seats on my Rav 4 for that very reason. I used to own a 1991 Celica with velour like seats. It was never a problem.
They offer the same seats in the Highlander but not on the Rav 4.
My son has a 2001 Celica with the same problem. We used Bissell's Little Green Clean Machine. It is primarily used for for cleaning upholstery and spot cleaning rugs in your home or auto etc. It has its own special liquid cleaner that you dilute with water in the machine. It sells between $65-$100.00.
It has a small turbo rotating suction brush or just a plain suction attachment. You just spray on the solution through the vacuum suction attachment and immediatley suction up the cleaning solution. It gets the water spots and any soiling out from the fabric or rugs and suctions the majority of the water/solution out and the fabric of the car seats dries in a few hours with the windows open. They make a prespotter for difficult stains. Of course there are some stains that will never come out depending on what they are and how long you have allowed them to set in the fabric.
I bought Scotch Guard protector for the upholstery but as of yet my son has not applied it. Usually when I have used Scotch Guard protector before on car rug mats, couches, chairs, carpets etc; the water, milk, juice or soil can be easily blotted up as it beads up on top. There are several different Scotch Guard Spray products just be sure to get the right one for the fabric you are trying to protect. Don't forget to thoroughly vacuum and clean the fabric or rug first.
One would hope by now that Toyota would have corrected the problem or stopped making automobile seats with that fabric.