Well if theres anything I can say they are really not that old School, seeing as the drumstick was being used just as much if not more than brushes were being used at certain time periods. I personally like to use them on quiet jazzy parts of music, they can also be helpful in latin grooves.
I find them necessary to a drummer especially if your planning on exploring all aspects of drumming.
If you really want to have as broad a musical range as you can get on the drumkit, I'd say brushes are a must. I don't use them as much as I do the sticks, but they're good for when I'm doing swing kinda stuff. They're also handy for if you want to play more quietly.
brushes are great, and in my opinion, hard to get used to if you've played with sticks for a long time. there is a completely different set of techniques for brushes.
i like using them in the studio, for parts of songs that are lighter and need a soft, swishy sound. or for acoustic gigs.