I've recently been looking at tubs and some have obvious tread. I'm also curious about suggestions on tubs that are slip resistant.

most tubs have some sort of non slip finish. A shower is best for aging in place. You can also buy nonslip bath mats.

We have a toto cast iron and it has etched sort of circles on the bottom that keep it from being slippery.

We also have Toto cast iron tubs. The no slip grip (circles etched on the tub bottom, as daisychain01 mentioned) appear to do their job pretty well.

How often do the Toto or Kohler tub owners have to clean the non slip surface and what do you use?

In my Kohler cast iron shower pan, I use something called R.O.G.3 Its a spray. I can't remember how I came across it. Supposedly it is recommended by Kohler. It works well.

I wash my light gray shower pan about once every 3 months. I am the only one using it and I don't go barefoot. So it stays very clean. I could wash it more often, but I can hardly tell the difference. I clean the walls about once or twice per year, because I wipe the entire shower down after every shower with a microfiber auto detailing towel that I got at The Rag Company. Wiping down everything prevents any build up of soap and keeps all areas from getting moldy. I turn my fan on, and run about 30 minutes, when I start my shower and have never had any mold issues in the bathroom. Nothing steams up.

the towels I use for drying are: edgeless-avalanche-20-x-40-super-plush-drying-microfiber-towel

I hang it over my glass shower door and it dries beautifully. When I wash the microfiber, I wash on hot water with only other microfiber products. You don't want to wash microfiber with cotton, etc, because the lint from these other fibers are believed to "clog" the grabbing capacity of the microfiber. I used a squeegee for a few months and hated the process. A towel is SO MUCH easier IMO.

I also use body wash. But body wash is notorious for leaving a dark circle in the washcloths. So I switched to dark gray washcloths and don't notice.

Thanks for the valuable information. We made the switch to body wash and I no longer see soap buildup.