I'm going to chime in on this. I've been riding street bikes for 10 years or more, and just bought an 87 TW200. I was looking for a dual sport to explore some trails on.... and let me tell you, this bike is great for beginner or seasoned rider alike. Engine is bullet proof, and it's super low to the ground. Top speed of 67mph with the stock gearing. I just ordered a 15 tooth countershaft sprocket and a few different size rear sprockets, and I'm going to see if I can get 75mph out of it (which will make cruising at 65-70mph much easier on the engine)
The XT225 is also a good choice. I don't know who said the engine isn't reliable, but it's one of the most reliable engines Yamaha has made. Seat height is higher than the TW, and it's a better all-around dual sport with 6-speeds and an 80mph top end.... but it's also twice the cost of the TW on the used market.
Honestly, the TW200 is some of the most fun I've had on two wheels, on or off the street. It's impossible to loose traction on those tires. What other bike has a 180/80/14 series KNOBBY? What other bike can you scrape pegs or even get a knee out on... on stock knobbies? No need for a SuperMoto conversion to really tear the pavement up.
Seriously, if you have a chance to buy a TW, go for it. It's not powerful by any stretch of the imagination, but it's still a blast to ride.