Well actually I was talking more of Southern California as in below San Francisco, not LA, I hear Northern California gets weather occasionally. I'm on the "Central Coast" and there's lots of roads that would be uncovered most of the day but still ample sunlight. I imagine in the higher use areas there would be an issue of longevity as well as reduced light.
Most parts of the earth don't have massive dust storms and when it's not on mars we can clean them. The rovers were built for 90 day missions and they didn't feel a mechanism to clean the panels was important enough.
In Southern California we don't get much in the way of any real weather other than sun. In more rural areas where the roads aren't used that much, and if it's actually comparable to traditional road materials, it should stand up for several years. I'd say the real value is for rarely used roads in sunny locations; or where getting roads, data and electricity all in one is rather appealing.
Except for robots don't require sleep, or a place to live, or somewhere in the realm of 16+ years to become mostly useful, and I'm fairly certain that electricity is cheaper and easier to produce than the bevy of foods required to maintain a healthy human being.
A while back in a similar thread there was a link to a story about what happens when artificial intelligence can perform menial tasks, I thought it was quite profound.
It's a bit long but here it is: http://www.marshallbrain.com/manna1.htm
Two percent of zero is almost nothing.