I agree with you in regard to parallel tubes in the scenario presented.

However, the Titan's twin downtubes are not parallel. They form a triangle with the base at the bottom bracket. The twin tubes are welded together just before they meet the head tube and spaced far apart at the BB. The water bottle bosses span both tubes to add additional reinforcement. Disadvantage: you're adding an extra tube (albeit smaller diameter than normal) and hence some extra weight, plus the fabrication is somewhat more labor intensive. Probably not much, but apparently enough that the modern Ciocc Misfit titanium frame abandoned the double downtube design in favor of a larger diameter downtube (probably with internal reinforcing).

As far as the ride goes, on last Sunday's ride with the club I appreciated the Titan frame's vibration absorbing ride qualities. My hands occasionally go numb when riding my vintage Columbus SL steel frame Ciocc San Cristobal on the less-than-smooth south Louisiana back roads that I frequent, but I had no such problem with the Titan despite a more aggressive riding position.

Yeah, I think I'll keep it!