If you haven't ridden a KLR or DR, ride one. They're trucks. The don't work very well on the street, and are even worse in the dirt. If at all possible, ride a year or two old KTM, 450, 525, 500EXC, something of the sort. Very, very good in the dirt. Not so good on the street. WR250s are underpowered. If they made a street legal 450, I'd buy one (Yamaha or Honda). DRZ400s are OK, but not like the KTMs.
Ride a bunch of different bikes. Get the ones you like. $15k buys a couple real nice bikes, shop around, lots of bikes with almost no miles on them out there. And personally, I wouldn't buy anything with more than 10,000 miles or so on it, too many low miles bikes out there to buy something that has a lot of miles on it. One guy told me that his 80,000 BMW was just broken in. He was lying.