Personally I wouldn't.
To improve the idle maybe try getting a new pcv valve and replacing the original clip-on hose clamps with screw type ones. Cleaning the throttle body may be a good idea; I did mine by removing it and then cleaning it. Also after cleaning it complete a throttle reset (search alfaowner).
The JTS can have lots of different vibrations of varying magnitudes especially on idle. If it is not serious, the car drives alright and no error codes are present don’t go prodding around too much otherwise you might just create a real problem.
Yes there will be carbon in your intake; if you are as keen as I was you could take off your plastic intake (very annoying and time consuming) and clean inside the intake manifold. It is not really worth the hassle to be honest.
Real issues are misfires, engine shut off’s, stuffed cats, etc. None of those unfortunately can be cleaned by an intake spray.
I once used a fuel additive recommended by some guy in an auto shop as I thought it might help clean the engine. All it did was make the car run funny for a while and cleaned my wallet a bit.
A while back I posted a few suggestions to help improve a JTS engine here
and to be honest with you if I had my way and an infinite amount of time on my hands there would not be an original electrical connector left in my car.
I hope that helps.