No way I would bother with the stock nav, it is barely ok and such a pain to use compared to modern touch screen navs. Plus the hassle of updating to new map data, risk of burning the laser using copied data disks etc. The only positive is having the ability to look at the map as you are driving around, I have found the mapping to be suspect at best. I would go dynavin in a heart beat before attempting the stock retro fit.
In the 18 months we've owned the ZHP, might have actually entered a address 6 times on the stock nav and about 50 times on a hand held gps.