I agree. I think the approach should be similar to that used to come up with a wayfinding typeface, if we presume number tags should have their main characteristic to be readability from afar.

Here is a decent look at the approach Ralf Herrmann took when designing an improved wayfinding typeface: http://opentype.info/blog/2009/09/02/designing-the-ultimate-...

My first impression of these license plate examples was more or less 'flat design' aesthetics and branding was exercised on them. However, branding and looking good should be a distant secondary consideration to readability.