It would be fun to have a empty level without walls and such where you can build anything without limits or objectives.
Also where there isn't a "Succes" popup message which hides the stats (very annoying if your building rockets that go up to 40km)

Not necessarily now, but perhaps sometimes in the future, I think it would be a great idea, plus an addition where you can download other users levels.

The rims of one of the wheel types could be a different color in order to quickly distinguish which ones on the contraption are steerable.

When you press a button, it makes the vehicle jump wherever its placed. More for the use on the BOTTOM of the vehicle.

Individual sliders for every rocket. 

pistons, joints, rotors, ropes, balloons  etc, just so you could build about anything, from a helicopter or forklift to a simple swing. Game is looking awesome, keep it up.

i liked a lot of the game, and i am a more "enginner" focused player, thinkering on the smaller details to archieve better performance.

trying to fine tune some race cars here, got 5.80seg on the S turn course.
http://youtu.be/AvvhxrI0AuE

These are some older experiments with more heavy but stable cars
http://www.youtube.com/watch?v=nLhC8xEE6GA


The whole deal is: it would be useful to the player to have some "summary" of the current build.

* length of each dimension
* center of gravity (show in the model as an "ghost" marker)
* total weight
Tire grip could be somewhat tweak able also, if all these somehow "make the game too much complicated" you could implement some "expert mode", even if we need to thinker with command lines and xml files of the designs, i would love it.

So we can make aircraft!

Add some wing type stuff and air resistance so we can make planes. Helicopters would probably be too hard, they would just explode.