with the tto1 theres load of upgrades, some worth while some not depends on what u want the car for? a tt-01 with aloy prop and motor mount and ball barings all round is a good car to bash, things like the ball bearing stering set up helps with the cars slopy handaeling, and the carbon upper frame helps to stiffent the chassis twist a bit. its all up to you, what i would advise is to start with bearing, motor mount and alloy prop, run the acar for a while, then do the steering and see what u think, then the upper frame etc...... do each mod on its own, then drive the car a bit, so u know the diffrence it makes,
i like the tt-01 its simple and fun to drive, and theres loads of hop ups for it, you bank account is your limit :-p
here my current tt-01 project, not finished yet, waiting on a few bits,