I've read that article and disagree. I see a big difference in value on the used market in favor of the nav, meaning cars with nav sell for more.
I absolutely understand the value of it, and Lexus offers real time traffic in their systems just not on the IS. I've used the system with no real time traffic for years though, I don't really see it as a neccesity.
I've used the built in Lexus nav for many more years than you and I've used plenty of portable units. I would never spend one dollar on a portable unit, they hold absolutely no interest for me at all.
I guess we'll have to agree to disagree.