You don't need to bring in all new soil. However, anything you plant will do better if you amend your sandy soil with organic matter in the form of well-rotted compost or manure, peat moss, or leaf mold. Apply a layer 2-3 inches thick and work it into the top 6-8 inches of your soil. Otherwise, you are limited to plants that can tolerate your sandy soil and sunny conditions. I suggest you look for information about plants that are native to your region. Native plants, particularly prairie plants, have evolved in tough conditions and have proved their staying power. The list of native and nonnative perennials that adapt well to sandy soils includes wormwood (Artemisia), yarrow (Achillea), globe thistle (Echinops), lavender (Lavandula), salvia (Salvia), Russian sage (Perovskia atriplicifolia), and sedum (Sedum; Hylotele-phium).