2 things that contract gives you that unemployment or even subbing doesn't are 1: A classroom of your own which will look good on your resume for future employment, and 2: a way to build a routine and a work ethic. Sitting around collecting a check and waiting for a call can be an easy habit to get into and a hard one to break. Put yourself in the shoes of the hiring manager. If you had 2 candidates, one with full time experience and the other with some occassional subbing which would you choose?
I live in Georgia, home of the $47,000 teacher. The year I moved down here the state was ranked 49th in the nation. I haven't checked lately but I doubt they've risen much higher, at least without administrators changing the test grades to raise the scores (we have a major cheating scandal in the state) So if more money equals better results you'd have a tough time proving that here.