Its not worth buying a barrel kit for the purpose of being able to put it on a different gun, and certainly not worth buying barrels to change sound signatures.
The real reason for buying a barrel kit for the purpose of improving consistency which in turn does in fact increase accuracy. Choosing a barrel that is slightly larger or smaller than the actual paintball bore will give a smaller range of FPS, which over distance will help improve the accuracy of your shots.
Is it worth buying? Well on the tournament field where you'll be pretty much shooting a stream of balls rather than 1 ball at a time, and over a relatively short distance then you're rarely going to get the benefits you're looking for. Maybe out in the woods when you are trying to line up a shot, if you fire 1 ball to judge the distance, if you adjust and the velocity is consistent you should be dead on, whereas if the velocity was way off from the 1st shot, it would be much more difficult to line up a 2nd.