If discs did not need to be straightened every once and a while Park probably would not sell a Truing Tool. Everyone's disc may need some truing every now and again. I need to do mine but I keep forgetting. It takes a few minutes but easy easy.

Pull the pads and see if they are glazed over. If it's been a while since they were installed may be time for new pads. Check your disc for wear as well with a bike that old.