It runs lean, which is why it's not the best starter, and also you get that surging at higher gear low constant speed with small throttle openings. The reason it is set up lean is to get through the emissions tests, it's also got AIS (air induction system - which is worth getting rid off) which pumps air into the exhaust when you close the throttle in order to burn up any remaining fuel as you close the throttle. It's one of the last bikes to feature carbs as it's almost impossible now to get them to confirm with the latest emissions requirements.
Not sure what's been done to your bike - are there any receipts for work done?
Fit the K&N filter, I doubt it will do any harm or make any difference, but it'll last forever if you clean and oil it every year.
Ivanising is a bit different from K&N re-jetting as it addresses stuff like like by-pass hole sizing. Never mind the performance increase the bike just runs much nicer once the carbs have been ivanised. Plus if you went for the kit that mods the air-box too that'll make the most of your K&N filter.
Search the threads there's loads of stuff on Ivanising. There's info here - a bit technical but also a good overview to what the Ivans kit is about. fazerowners.yuku.com/topic/5715/Ivans-Jet-Kit-Installation-Guide-Very-Long-Post#.URF3RtWZzIs