I had two TW200's ... I loved them !! I was looking for another one (for under $1000 which is almost impossible) when I found the DR125SE by chance.
Since I don't have any seat time on the DR yet, I can't really compare the two. But I will say, it had plenty of power for my 6 ft, 200 lb frame, and I loved the huge tires. In fact, that was my favorite part.
Tires are Not hard to get, and nobody "adapts" other tires to work. More than one company makes the stock tires, and Bridgestone also makes the "street" version tire for that bike, which I had on my 2005, and loved as well.
Tank is not much smaler than the DR, if at all. But I do believe people had done an XT225 tank swap for more capacity.
Bikes are not seen for sale much, but since they made them from 1988 to present, if you are looking you can find them in all price ranges. I missed one on ebay for $30 last month. It sold for $955, my high bid was $925 at the end.
I did like the TW better than both my Yamaha TTR225 and my Honda XR200R
Quick note on batteries for the TW (since that is what I do for a living) ... you can swap out the acid-filled battery, and put in a sealed maintenance free battery very easy. I used the high performance YTZ7S, which I considered using for the DR as well, but just went with the YTX7L-BS because it is much cheaper