I don't know that I really beleive that entire kit only weighs around 10 pounds. I have one of their shock mount relocation kits laying in the shed and I bet just that alone weighs 5 pounds. Even having another 10 pounds over the front wheels is bad on a warrior though, part of the reason that they feel like such a tank compared to the newer bikes is because they're so front end heavy from the factory. Good for hill climbs and trail riding, bad for handling, jumping, racing.
I've been riding for about 10 years, and for tight trails like you're describing, I would take a narrow, stock width quad over a widened one. I don't know how to explain it, but the width doesn't really play that big of a role in your speed in the woods, at least the way I ride. It's kinda strange but I can actually run faster lap times in tight woods courses on a little 250 honda than I could with my warrior, and even with the 700's yfz-inspired suspension i'm not much faster than my old honda recon in the trails. It seems like speed in woods riding is about 90% based on rider skill, 10% machine.
If you still want to widen it, keep an eye out for used a-arms and shocks. I've seen them for sale on ebay as a set before at about $350 for everything, only $150 more than a DJ kit and including aftermarket shocks.
A set of properly set up shocks will actually help your cornering a lot more than just extra width will, the stock shocks are simply an oil filled pogo stick in comparison to modern stuff. You would be amazed how much of a difference in your handling it makes, but it reduces body roll and it maintains tire contact much better, the stock ones will send you bouncing all over the place, and you can't maintain speed through a corner if your tires aren't in full contact with the ground.
If I were to buy another warrior and set it up for trails it would definitely stay stock width, possibly aftermarket a-arms but stock width or +1 at most. Good mid-level aftermarket shocks (Elka, Race Tech w/o reservoirs approx $500), and send a Banshee rear to Race Tech for a revalve. Then good tires, don't cheap on tires, all the suspesion and width in the world are useless if it won't stick to the ground. I like Razr 2's or Holeshot GNCC's for the front, they stick like stink on ****, and for the warrior i'd go with a less aggressive 21 or 22" rear, probably original Razrs or Holeshot XCRs, unless you hit sticky mud then i'd go with Kenda Klaws. The X-pattern knobby tires are good until you hit mud, then everything except the real aggressive ones don't clean out, they just turn into a big smooth ball of mud spinning and going nowhere.
Go with either stock Yamaha wheels or .190 aluminum aftermarket wheels, the cast wheels like ITP C-series are also pretty tough but the lip of the rim can crack if it takes a heavy hit from a rock, the .190's will just bend and roll the lip which can be fixed.
That's my opinion, at least that's how I would set up my own for woods riding. I put a lot of money and time into my warrior, some of which was worthwhile and some which was a waste to me, so it's an experienced opinion.