Actually I am very familiar with the KDX, although I don't own one myself, my bestest buddy and riding compadre does own an 04 KDX220, and i have ridden it many times from brand new off the showroom to it's current heavily modified state. I also have had the opportunity to ride a 90 something KDX250 that had the Blue inverted KYBs stock. They were crap too but sprung better than the stock KDX forks. I agree that the excessive underhanging outer fork legs can be problematic in rocky envirornments, in NW Florida they don't pose a problem. either way He had his suspension revalved with Race Tech valve emulators and sprung for a 180lb rider. I took it for a spin, and at that very moment wished that I too had bought the KDX220 instead of my KX250 and just had the suspension done and added a Vforce reed block, fmf gnarly and Q, ands a set of Dunlop MX31s.It would have saved me $2000 in mods I made to my KX250 to accomplish the same thing. But in all honesty, my KX will destroy that KDX, but his KDX sure is fun to ride and way better than it was stock.
But like I was saying about the upgrade...
Yes: an inverted fork is a more modern design and more adjustable, the spring rate from any KX is probably closer to the shock on the KDX
price though is what I'm debating
Stock KDX revalve with valve emulators and springs cost him $550
set of KX forks with clamps and a front wheel used on ebay will run about $400-500+, then the revalvin to match up both ends another $300+/-
So really I suppose it's one of those "eyes of the beholder" things