The Plaza is a great site for art and culinary festivals obviously. The library is here, Scottsdale Center for the Performing Arts, etc. There are some great restaurants, too. But the park itself is just gorgeous.
If you have never been to the Plaza when there is no big event going on, that is the time to go. The park is beautiful. There are so many fountains and gardens to meander around. It is beautiful. You almost forget it's a hundred freakin' fifty degrees in August.
Visit at night, too, after a nice dinner downtown. We did that on Saturday evening, and it was virtually deserted. Such a nice place to sit and remember the nice things about living in the Valley--January with no jacket required!