Well, I've been chewed out because someone walked into my bike rack when the car was in a parking lot. Car and rack were stationery. On a clear day. I figured that was their problem.
I have to agree with @
Koyote, though; you're just advertising "here's a bike to steal" when you leave it on the rack and drive around where you're not driving to ride the bike.
Assuming from OP's user name she's in the desert, an occasional wipe with a rag and perhaps Pledge will clean the dirt off most parts of the bike. A different rag to wipe the chain off is probably all that's needed if you're using a dry lube. Of course, when the bike gets rained on, you may want to dry it off ASAP and give it a taste of oil (aka wet lube) to prevent rust and hit the cables with some lube.