Some of the recommendations are iffy. The Spiral Jetty is cool to look at as you drive past on the way to Wendover but I can't see making a day of it just to see it. If you are going to drive out to see the jetty you may as well go a bit further and see The Tree of Utah.
If you are going to do a day trip I would recommend Cascade Springs up American Fork canyon.
I like the Red Butte Garden rec but would add that it is a spectacular garden display and should be visited during the day as well as catching a concert at night.