RDD hit the nail on the head, your luxury tax won't promote interest/activity/involvement from the less interested owners, it will deter it. "The less I do at this point, the more I'll make later."
I'm on board with your smaller divisions will increase prolonged interest by always having a smaller mountain to climb. Another idea might be to award the high score for the week or something like that to keep teams striving to put their best team on the field. You could supplement that pool with your FAAB payments, i.e. the more you spend to improve your team throughout the season, the better your team will be (in theory), and the better your chances of winning the weekly award. Return on investment.
In my leagues we treat all money as real, the auction draft, fees for transactions, and FAAB dollars spent, all actually has to be paid and all goes into the prize pool. It goes to the winners though, not the guys who spent the least. You don't want to create the Marlins and Pirates of the past decade.