There are no major issues with those bikes and that Yamaha 4-stroke is the most reliable of all the the brands. If it's clean and cared for, and you feel the value is equal or better than your R6, I'd go for it!!
I had an 04 WR and an 09 WR, both were used as trail, street tard and track tards.
I liked it as a trailbike, but it is a bit heavy in the tight stuff...along with the other comparable 450cc thumpers.
Track was OK, plenty of power, smooth running, but you'll have to mess with the suspension a bit coming from woods riding to track riding.
Street riding was pretty good also if you do rides less than 100 miles in a day. Again, plenty of power and smooth running! My only complaints with both for street riding was a hard seat and small gas tank. The range was about 50-60 miles on a tank.
It's always a plus having knobby tires/wheels and supermoto tires/wheels for it as it can be a 4 season toy if you have the desire to ice ride with it