On my personal TSPP, the garage door really doesn't work, and I haven't bothered fixing it at all. The switch for hitting the door still registers most of the time, yes, but it doesn't necessarily (*maybe* one time in 20?) open up near enough for the ball to pass through to award the Mystery Award or send the ball to the upper playfield. This greatly, *greatly* affects the way the game is played, as you can't afford to just basically ignore the third flipper ramp shot any more...you've *got to* hit that shot in order to make it up to the Living Room to start modes, lock balls for multiball, get super jackpots, etc.
The one caveat to my pseudo-mod (read: kind of lazy about fixing it, but enjoying the resulting change by not doing it) is that the garage door will sometimes slightly open, enough for the ball to get behind it from the Quik-E-Mart shot. This can be a pain, but it's part of the challenge, too.
I've found that playing this way really, *really* makes multiball special, and when I achieve it, I'm feeling pretty good about myself. It also makes playing modes, when you can start them, much different, since the clock is that much more difficult to reset/add time onto.
Meh. I'm not married to the mod, but it kind of fascinates me, so I leave it there. No one plays it but me, so who cares?