The scene with Saul saying "you don't try to win the lotto twice" brought up the issues I was feeling earlier, that Walt has an opportunity to walk away clean here and he's not taking it. I'm not sure his excuse of "Well, I owe $40,000" is enough. 40K doesn't seem like that much to have to risk everything he's risking by starting a new enterprise, buying new equipment, chemicals, buying people off (how much is this all going to cost) to take on the cartels and putting his family Back In Danger. At least, $40K doesn't seem that much when the car wash is profitable on its own (per Skyler) and he has years of healthy living ahead of him.. Hank can walk, they're probably at the tail end of those bills. Is Walt really going to go back to war over the cost of the Mustang excursion? (And how has Skyler not yet noticed the refund they were due from the dealership never materialized?)
I feel there must be something else, probably the return of the cancer, that's motivating him here. I don't buy it's just pride in his product and a desire for $40K just yet. If he really has a profitable business and many years ahead of him, I don't buy him jumping back in with both feet.