You are correct, in a metal lower temperature leads to higher conductivity (fewer phonons to disrupt the mean free path of the conduction electrons). In a semiconductor, however, thermal energy creates more carriers and adds to the energy of those carriers to be able to cross the bandgap. So for a semi-conductor higher temperatures lead to higher coductivity and less electric potential necessary to cross the p-n junction in the LED. Unlike a metal which can be super-conductive at 0 K, a semi-conductor becomes an insulator at 0 K.
That being said, it is possible that the heads up display does need to warm up before it operates efficiently, although I dont know anything about this display.
(sorry for the detailed post. I like to vist this site to learn about nissans and the 240, but since this is a topic I know about I figured I would help out <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/thumbs-up.gif" border="0" valign="absmiddle" alt=':thumbsup:'> )