I don't think you can compare the engine technology or the suspension of the DRZ to the WR at all. If you were going to bring the DRZ up to par with the WR in these categories you would have to spend a lot more than a grand to bring it even close. Then to shave some weight you are talking mo' money. Now if you wanted to ride a bike mostly on the street then yes the DRZ is probably a better choice, but who wants to ride themselves to sleep on the street when you can rip up hills on a WR.
After reading his post again... he owns a KLX (DRZ). If he sells it to get a WR he'll loose a big chunk of money.
He should look at the Dirt Rider Magazine bike buildoff for ideas on mods (within reason... geeze... they went nuts). Link
Then ask the guys that did the suspension and power mods what they would do if their budget were about $2500 and he wanted a WR450 beater. I'm guessing that's what the minimum difference in cost would be after selling the KLX and buying a WR.
The nice thing about the mods is that the cost can be spread out. But if it costs too much to get something more like or better than the WR... get the WR.