Interestingly enough, James Lileks touches on that this morning. Granted, he's the man who scours old postcards and noir films partly because he digs all that neon and urban "visual pollution." (Scroll about halfway down for the relevant portion of his post.)
Writing about the Highway Beautifcation Act of 1965, Lileks says: "How messy it must have seemed to the advocates of the clean, spare roads; how crass and vulgar, all those blinking stars and buzzing neon tubes and backlit enticements. TV. PHONE. POOL. The idea that these signs were actually examples of a uniquely American art form would have been met with rolled eyes and an exasperated sigh. The ideal road, apparently, was a feature-free corridor punctuated by rational International-Style pavilions every 42 miles, freed from the garish intrusion of commerce."
Amen to that, brother. I've spent a lot of time on our highways and interstates and I'm quite fond of those billboards that have stood the test of time. I used to drive from Louisiana to New York during college and billboards not only told me when to expect the next Motel 6 or completely ridiculous tourist attraction, they kept me entertained. There was nothing worse than entering areas in the Northeast where such signs had been removed, toll booths and other barriers set up at every exit ramp and the only option for food was the government-sanctioned Roy Rogers sulking in the median.