Having been an IT professional for 10 years now, my general feeling is definitely along the lines of "if it ain't broke, don't fix it."
I read one account on the web of Tiger engine failure that someone blamed on the K&N filter, saying the particles it allowed through were too big. The guy came off like a bit of a wingnut, but I've also seen hard data that says oiled cotton filters (like K&Ns) pass much larger particles than oiled foam filters (like stock or Uni). IIRC, oiled paper filters block the most grit, but they also pass hardly any air. Oiled foam is almost as good at catching grit as paper, but passes way more air. Oiled cotton passes more air than any other filter, but passes more grit by a big margin. Stacks, of course, pass the most air & let all the grit through as well. This is all from my memory, so take it with a grain of salt (or a bottle of Newcastle!). Anyway, what I got from the scientific article was that foam catches almost as much grit as paper, but passes almost as much air as cotton. Hence, I'm sticking with stock.
That being said, filters do get dirty & need cleaning. It may well be worth it to take the airbox apart & clean the filter. Uni cleaner & oil is the right stuff to use on the stock filter.
Sorry if it's not what you want to ear, but if your airbox is on the verge of cracking it's probably time to replace it. I'd give it a try. If it doesn't crack & you get the screws out, clean & oil the stock filter & button it back up. If it does crack, get a new one.