Quit your day job, then you'll be motivated :-) Okay probably not the most sound advice to follow there. But it is true that whenever you feel comfortable financially you tend to naturally lose some drive. Definitely happened to me.
Do you want to do your day job forever? Do you like 70 hour weeks? Or would you far rather rake in the cash whilst working to whatever schedule you want? If you don't work on this new game, you're essentially waving goodbye to that dream. I can't tell you this game will definitely be a huge success, because I don't know. But I can guarantee that you'll be stuck working for crappy employers for the rest of your life unless you knuckle down and start releasing games again. The opportunities for indie developers have never been better, but it may not stay that way for long. Get back in the game while you still can.