I used to own a Tomtom rider. It's so useful for getting around towns that you are not familiar with. If you do any touring you'll want one unless you like getting lost. By getting lost I mean sometimes its fun just finding your own way from point A to point B. Is it a killer? Hmmm not really for me, it allowed me to plan better, I knew that if I wanted to be on the coast by 9AM I could do it, and you can always turn it off.
If you are looking for adventure try getting a walking unit and only pull it out when you are totally lost and have to make up time. That should offer alot of adventure and you'll always have a way to get home when you get totally lost. I've accidentally ended up in the wrong county so I see a GPS as a life saver.