You all may have not considered this, but hull integrity is the signs of age on your ship. How about instead of repairing it whenever it can be repaired, let it build up and pay for it all at once.That'll not only be more realistic, but increase your immersion. Ships get old, and digging into the frame of a ship to shine it up isn't cheap.
The lower your hull integrity, the lower your base hull strength. If you have 0% hull integrity and 100% hull, you only have 70% of the hull strength of a ship with 100% integrity and 100% hull.
No, it is not realistic, because if the price of 1% repair of the hull integrity is 0.5% of the price of the new ship, it is better to fly to the sun as soon as the hull integrity drops to 90%. Somehow, I am missing the "immersion" in it.