I would recommend getting the warranty. The Busa is not a Honda, I am not knocking Suzuki but the GSXR's have always been just enough more maintanance happy than some of the others. You have a 1300CC engine cranking out a crap load of horses, things are under alot of stress. These engines are basically "racing" engines, high compression, close tolerances, high rpms , its a natural that something is going to get fouled up sooner or later.
It could end up being a waste of money, and it is true that mod MAY void your warranty, but many mods will not.
IMHO the warranty pays for itself in peace of mind if nothing else. While the Busa is several generations old it still has some problems, starters self destructing on the 02's a grip of issues with the 99's etc... If you plan on keeping it long term, and over the first five years nothing craps out, then good for you, you have what will most likely be a trouble free bike. But if it goes the other way the warranty could pay off big.