Actually, the stock clutch is pretty damn good, most of the engine builders recommend using the stock yamaha plates and friction pads, just with an extra steel plate (due to a flaw in the clutch design on yamaha's part) and heavy duty springs. If you want the best of the best you can spend $180 on a DP clutch kit but that's really a waste in my opinion. EBC clutches are good for the money, but in my opinion, stock is still better quality and durability.
When you take your clutch apart you'll probably see that the clutch really doesn't look worn down that bad, it'll make more sense when you take the clutch apart and see how everything works, but there's a design flaw (or possibly intentional, but it sucks either way) the clutch pressure plate will bottom out and run out of travel before the friction plates have been completely worn down. When my clutch started slipping and I took it apart I found that the stock plates were probably only at half life, just adding another steel plate somewhere in the middle of the pack gives it the extra thickness it needs to get more life out of the friction plates.