I've never had an emissions test on a bike MOT?!
With regards to the mod itself, the following is my opinion after looking what the respective parts actually do under the particular conditions they are meant to work in. I reckon there is no performance gain. The parts that are recommended to be removed are those that stop fuel overflowing when the system is under a high vacuum - for example when revs are high changing down gears into a corner. When under acceleration (when you need power) the parts do nothing, so having them there or not doesn't matter. When under heavy braking at high revs on a track day, I have found some spluttering (albeit very minor) when i initially hit the throttle to exit the corner. This is with the parts removed under the recommedend mod. So from my findings all there is is a performance deficit and it does not make the engine fuel better - the ZX7R carbs are duff to start with. The bikes are set up to be lean from the factory to get the bike through the emissions tests before Kawasaki could sell them, and get richer as the mileage increases due to wear in the carbs.
This is just my opinion, not necessarily the correct one!