I've been called a pig on a 350 before, but I don't believe that they are pigs on gas. Of course, they are not going to get as good m.p.g. as the thrifty 200 but manly, fire-breathing horsepower always comes at a price. On most rides, I spill more gas when the bike is upside down in rock piles than I burn in the engine.
The early TW shared the same forks and brakes as the BW200. I imagine the BWs would have gotten a disc front brake along with the TW had the line not been terminated.
The rear shock is also interchangeable between the TW200 and the 350, although the parts numbers don't match.
All three of the bikes utilize the same Female Repulsor. The 80s did not come equipped with a repulsor and as a result are often considered "cute."