First I'd ditch the slip on. It doesn't produce much power gain, Duals, any set will help you much more. Second, the intake you have is ok, but you will get more power out of an FCI, and the great thing about an FCI is the more add ons you get, the more power it will help you produce from those ad ons. Next I'd look into a Cam, Hot Cams stage 3 was recommended to me, but I'm still researching.
My buddy has an 09 YFZ 450R and he's got quite a few mods, Performance wise, it's the big 3 with an MSD blaster, K&N, and DASA exhaust, he also has an older YFZ intake cam. He produces less HP than me, but we are incredibly close racing. In a very short race and off the line he's got me. It all depends on Shifting, and launch, the raptor has to short shift, and most of the time I'm better starting in second, if we have a long enough race, once I hit 4th I'm pretty much gone, but we need space for that.
You shouldn't have any problems selling your stuff that you have now.. someone out there is wanting to be cheap and buy slip ons until they figure out they need more.. Tech quad shop, and KB both have great deals on Barkers, DMC's, Dasa Duals, and FCI intakes!
Here's an example, my buddy has a Raptor, PC3, and Barker Duals, with a ModQuad K&N, he ran 48HP after dyno tune, Mine, same Dyno guy, has barker duals, PC5, and FCI intake Ran 52.61 HP. Only difference is the PC5 and FCI, mostly I attribute the gain to the FCI.