You're right that the amount of radioactive material is too small to warrant serious worry, but please distinguish between isotopes; Plutonium-238, the isotope

You're right that the amount of radioactive material is too small to warrant serious worry, but please distinguish between isotopes; Plutonium-238, the isotope used in the rover, is a very powerful alpha emitter. You definitely don't want to inhale more than a trace amount of it. (On the plus side, a piece of paper can shield you against alpha particles, which makes this one of the easier-to-handle isotopes -- a good choice for radiothermal generators like this.)