Actually I've broken spanners (reasonable quality Kamasa ones) on bicycles before, so I'd hold fire on getting a Ti one personally
Actually, I believe that the reason that the bike tool was made of titanium was not because of weight but because of sweat. I carry a 3L hydration pack, a bottle of sports drink, light rain jacket, keys, pump, leatherman kick, and my cellular when heading out for a 3+ hour ride. It seems like a lot of extra weight but I like to be prepared. Adding a small tool that services almost everything on my bike is really no bother even if it were made of tungsten. I carry the tool in my jersey pocket and I have noticed some rust on the driver bits already. That made me think of why the tool isnt made of steel. It would turn brown in about a week.