One or two other observations -
Many of the people visiting/traveling thru DV are tourists, and a high percentage are non-English speaking. So, no matter how much you improve signage, how does one account for signs in French, German, Korean, Chinese, Japanese, Russian, etc, etc. These tourists are not expecting to contend with a running/cycling competition.
And John - not to nitpick, but your statement - "for the most part the roads in Death Valley are straight and have few visibility limitations" isn't entirely accurate. Certainly there are many miles with long sight lines, but many sections - like descending into Badwater from Lone Pine, or working your way in/out of Panamint Valley from Trona, contain many hairpin turns with very little tolerance for swerving.
Also - keep in mind there are other running/cycling events scheduled there other than the mega-events mentioned here. I've encountered smaller events for which there was zero warning/signage.
