In well-fertilised soil, grass grows more vigourously than wildflowers, and consequently the grass will smother the flowers. Because of that, it is easier to grow wildflowers in poor soil. You certainly don't want to 'enrich' the soil.
Whether you want to go to the trouble of removing the top few inches of soil altogether is another matter.
If the area has just been grass, and has not had any fertiliser added to it for some years, then the soil may already be quite poor.