The Honda factory nav units are actually pretty damn good. I've played with factory Ford units, Nissan, Benz (in europe though), and the HK trafficpro, Pioneer Avic-1, and the older Eclipse one. This Honda one is the most accurate and best one I've played with yet in almost all areas. Second is the trafficpro. Despite no map and being pretty much just voice, arrows, and distance, I like the actual routing from the trafficpro the best. 2 reasons, it wasnt afraid to use major backroads where others insist on staying on interstates and highways as much as possible despite mode setting, and it also had a no tolls option for routing which really meant no tolls, period, instead of just 'minimize tollls' setting that still took you to them without even a warning like most others. If the Honda would do "no tolls" and really stay off those roads like the trafficpro instead of this minimize toll bs, it would be as good as nav gets at the moment. Anyways, the Eclipse one does have a lot of features and toys on it for that kind of thing. I dont know much about the Kenwood, but I'd go with the Eclipse.
I think throwing away the $1500+ on the price of the car by ditching the stock nav unit, and dropping another $1500+ on an aftermarket one is A LOT of cash just to play DVD's.