I've used quite a number of items from Spa day, so even if you don't take your sims to the spa you still have the option to get a spa treatment at home using mud baths and soaks in your own bath tub, meditation and yoga.
The decor is very nice and I use a lot of them in sims homes. Got soap dishes, a tray to make drinks, nice cabinets and counters, end tables, coffee tables, wall toilets (good on community lots and public areas), fancy fish tanks, wall lights, potted plants, wall fountains in different sizes, incense burner, candles, a more modern small stereo, new stairs, wall paper and flooring, windows and door, etc. Has a nice sleek look and modern feel to them.
Then you have more new fitness related clothing in CAS for men and women.
I take my sims to the spa maybe like once every sim week or so at best, least for my sims that are workaholics. Any families I tend to use the spa stuff at home. Can really snazz up any bathroom with these.