Jerry - I alternate between a Garmin eMap and eTrex Summit (both use the same handlebar mount) on my OSS bent. Although either will get one back to the car, the eMap is really nice for figuring out where the heck you are, or how to get to someplace specific from whereever you are.
Just for giggles, I put an IBM Thinkpad, external powered speakers, Delorme USB Earthmate and 12 volt deep cycle boat battery in my Burley Nomad trailer, and towed it around for a day... Not very practical, and I ended up getting paranoid thinking that someone would hear it telling me when to turn, and think that I had a kid locked up in the traler with "with all the windows closed", and turn me in. I was still trying to decide whether to tell them that the kid was shy, ugly or an albino, when the battery finally gave out.
Like you, I've also looked and haven't found any precompiled Garmin waypoint lists for bike routes, so I ususlly end up "wandering", and never save anything.
John