This is a discussion of some generalized robot requirements for some applications of interest (to me).
While exploring in person is interesting, there are times you wish that something else could do some of the tedious footwork. Perhaps you are looking for artifacts of some sort. Rather than spend a lot of hot dusty or damp rainy days trudging around until you see something that looks interesting, you could control the robot from the relative comfort of home.
I've driven enough robots around now to know that having an autonomous searcher that automatically traverses an area in some systematic way is a pipe-dream. You sort of have to count on a (at best) 1:1 ratio of "operator controlling time" to "robot operating time", although, you your controlling time may not be simultaneous with the operating time. That is, the robot isn't a time saver, per se. What it could do is save the time and resources getting to and from a general area. For instance, one could spend an hour each day, moving the robot forward a bit, picking strategic things to look at, etc. (This is the generic Mars Rover scenario... Most folks don't realize that Sojurner's top speed was 0.6 meters per minute. That's a blazing 1 cm/second, and I dare you to move something by hand that slowly.)
Some locomotion alternatives are discussed here.
Driving a remote controlled vehicle is fun. It has to move fast enough to be interesting, but not so fast that it's dangerous. The robot is controlled in nearly real time, so the remote control link has to have sufficient bandwidth to do this. The toy could also serve as a testbed for developing technologies and algorithms for the more sophisticated exploration rover.
I've thought of this as a flying robot of some sort that can carry some sensor package over some terrain. The sensor might be electromagnetic (ground pulse radar) or imaging. For this, some form of autonomous scanning might actually be useful and feasible.
Trail standards: http://www.nps.gov/romo/Backcountry%20pdf%20files/F%20-%20Trail%20Standards%20Summary-Detail.pdf
Rock Size distributions