I seems as though all his outlets are somehow closed off (physically or mentally) such that his last avenue for risk and excitement is the gambling (or starting a surely losing war with NY.) Regardless, the "fun" of this life wore off some time ago for Tony. All that is left is the financial reward of being boss which Tony seems bent on harming one way or the other - through gambling, poor placement of capos or a disasterous war with NY.
I'm wondering, what do you think constituted the "fun", the other rewards of being boss that fell apart as time wore on? What I'm curious about is, if the financial reward alone didn't warrant assuming the position as boss, what were Tony's other motivations? I'm not entirely sure myself, but I raise the question because understanding his conception of the rewards could shed some light on the recent downward spiral of self sabotage.