Interesting topic. I have a Nuvi (don't know the model number) and just recently I noticed that somewhere in the settings you can set it for walking and/or bicycling. Can't really remember which, but I would think that anything you can do in a bicycling or walking mode you could do in the other.
But I haven't checked out the battery life. I'm going to check that out. Around where I live there's absolutely no need for a GPS other than to track rides for fun, but I often rent bikes and/or wander about while traveling and having the GPS might be handy or at least fun.