The nav in my 01 is pathetic in comparison to a Garmin. When I go on a trip I use my Garmin because of that. Perhaps the 06 had a better GUI but I personally would not spend that type of money to upgrade.
You may also open up a can or worms when you tackle this. If you get all the parts as described you should be fine. Running the harness from here to there will be a job in and of itself.
2002 MDX Silver 357,000 miles