I was just reading this article on how Curiosity's aluminum wheels are getting pretty dinged up. Usually titanium alloy is considered an upgrade from aluminum alloys in most applications, from aerospace to bikes to sporks. The "usual" downsides are that it is expensive and difficult to machine. However, those seem like less important factors when you're NASA and the plan is to send an object to another planet and drive over sharp rocks.
Aluminum is less dense than titanium. For the same mass, the 0.75mm thick aluminum would have to be replaced with 0.45mm thick titanium. Although the titanium sheet would be stronger in tension, it would probably be more susceptible to tearing from a point load like driving over a sharp rock.