My two cents.
The Thunderbird 2, ball lock is a given I think. :)
It would be cool to see modes start with getting a ramp shot or two or hit a Jeff Tracey target/toy.
You could have missions/modes that require one or more of the vehicles to participate in the mission/mode.
To activate the vehicle you could have different shots.
Thunderbird 1 could be a ramp shot or a vari-target.
Thunderbird 2 could be two stationary targets or hit the TB2 toy twice.
Thunderbird 3 could be inline targets.
Thunderbird 4 could be a line of drop targets.
Thunderbird 5 could be pop bumper hits.
A wizard mode could incorporate all the Thunderbirds with a video mode somewhere thrown in.
To complete the end of the wizard mode maybe?
Divertable ramps could save you dollars and space in the machine whilst introducing deeper game play.
RGB led lighting would be pretty cool. You could have something similar to Space Station with the condition green and red etc.
Mike, are you getting some professional advice from any pinball designers?
The reason I ask is that I just recently read about Ben Hecks issue with the Lost pinball he was making.
It turned out they made a great looking pin that played terribly but after getting some pro. advice he now has a much better understanding of pinball physics.