I'm cool with the "I want to change it because I can" theory, I've done it many times.
But most of those times, I learned "if it ain't broke ~ don't fix it".
Most aftermarket valves offer more in learning experience than performance.
I've found that a valve is a valve, and it's better to fine-tune what I have rather that start over with something different. Many of the moving parts wear in rather than wear out, gradually getting smoother as they adapt themselves to a particular set up. Even springs start out stiff and work themselves down to a consistant pressure through use.
It all comes down to balancing your springs against your air pressure. A valve with a higher flow will need pressure and less spring tension to allow it to stay open long enough to accelerate a paintball to 300 fps. A smaller ID valve will need higher pressure to allow the same amount of air through, and stronger springs to balance the higher pressure.
Now I'm just talking too much.