The farthest I have ridden my WR on the road was from the campground just out of Moab with the gas station to Green River where the truck was. My ass still hurts and that was in November right after I wrecked. I couldn't stand very well because of my knee or I would have. What was that...maybe 70 miles or so? Will the WR go that far, sure, was it comfortable, no. I don't know how those guys that turn them in to SM's like to ride them on the road that much. Another thing with WRs is that they sputter at higher RPM if kept at a constant speed. Some claim it can be taken care of with jetting but my WR is dialed in and it still does it. Most people will buy different ignition boxes to fix it. I read an article on the internet saying that Yamaha did it to cool the engine at higher speeds that are maintained for longer periods of time. On the trail it doesn't do it. I don't make a habit of going more that 10 to 15 miles on the roads before I hit the dirt.
With all that being said, Greg is completely right here. The WR is a very capable bike off road, especially for places like AF or Moab and if the riding you do is on the road long enough to get to the dirt and having fun in the dirt, you'll love it. If you like the dunes, get a YZ or CRF, better yet find you a big bore oil burner. If you spend more time on the roads, get yourself a Tiger or something like that. Caleb had a nice Husky that would be perfect but off road for long periods of time it will ride you.
I bought my WR because it suited my riding style perfectly. I'm too old and fat to ride tracks for very long. I leave my house and in a couple of minutes I can be heading up Farmington Canyon or across the Fire Break and in 10 minutes I can be at the B. I have added the Revlok for the tight trails and a YZ exhaust cam because it helps feed my OLD ego and I can rip with the YZFs and CRFs at the dunes. It just hits so much harder and I like that feeling. The suspension fits my riding style now and I really like the bike. I am going to make a seat fix as per Gregs instructions and some lighting changes and then it will be perfect.
Tyler (pELYgroso) rode my WR the other night after we replaced his fork seals in his WR250Z(oil burner). Maybe he has an opinion now of how a WR450 is to ride and can post it up here when he gets back from Moab.
If I was to do it all over again, I would do the same thing. Keep your eyes out, watch Craigs List, KSL, etc and you will find a deal. Greg turned a real eye sore into a very nice bike and he can ride it for a few years and still come out ahead.