To me, this whole GPS issue/problem could solved by future updates to the kernel or an updated OS like ICS(when it comes). To the op's point that the problem with the GPS and Prime is a design flaw but how do we know this? Initial release of the tablet was 11 days ago and now people are sending the tablets back because GPS doesn't stay locked for an extended period of time. I don't know about you but I sure didn't buy this tablet as a GPS Navigation unit. It does the simple map information when data is connected.
Now, yesterday I tested Google Navigation on my Prime and after resetting my A-GPS with GPS Status, I was able to get a lock with 10/12 sats in 3 minutes. That, imo, is pretty good seeing that I don't have a cell towers aiding in my coordinates. Now it did lose its lock after about a mile but after having a rooted phone and running AOSP roms quite a lot, this really isn't news to me. Like I stated before, future updates could possibly solve this issue.
After looking into the Google Maps application, there is a setting, storing cache data when you don't have a data connection. My guess, since I haven't tested it, is that once you have point of interest(Point B) determined then the cache will be stored on the tablet/phone so that the application has reference to go to when there isn't a data connection. Well, unless you are tethering the tablet, then obviously you won't have a data connection. Now a reason this may be helpful is when a reroute happens. How is the tablet, without the tablet having a data connection, going to reroute? So the stored cache will hopefully aid in this scenario.
I'm not sure if the Prime has a design flaw or its a kernel issue or an os issue..... and maybe, GPS will never work as it should but imo, I don't care if Google navigation never works. I didn't buy this tablet as a Navigation unit. Other than the initial problems with the GPS, this tablet rocks and highly recommend buying or keeping the Prime