I believe Rahab's virtue in on recognizing the Lord as such 2:11 "for the Lord your God, he is God in the heavens above and on the earth beneath", not because of her career or the fact she hid the spies.
I believe her significance is because women and prostitutes where considered the lowest of the lowest and the cast down in the society of Joshua's time (not anymore - thank God). the lowest downcast recognizes God's power and purposes. All the others that heard her and believed and lodged in her house where saved. She was a good witness to the good news!
Is she a type of John the Baptizer?