I used to like the idea of being spontaneous and also did not fancy using a sat nav however once you have tried to get a room somewhere to find you cannot get one as they are full due to a local festival, over priced (Italy circa 2001, 11 pm in a roadside motel style @ €175 comes to mind) , you cannot find one (sounds strange I know but there are miles and miles of nothing in parts of Germany - well apart from excellent scenery) and to book into somewhere and find it awful, we now do as above - i.e. find a final destination and plan route around it. 

We use a combination of Biker Friendly accommodation on www.thebikerguide.co.uk and if there is nothing in the area we want we also look on booking.com.

We did a trip a couple of years ago with the final destination being Colditz Castle, which you can stay in. Went in July for 3 ish weeks with everything booked, set into sat nav and you know what - thank goodness as it rained everyday but one. We would set off with the next place in the sat nav - take off route when we wanted and arrive at destination stress free.

We stayed at some great places, travelled fantastic roads and routes, ate well, found our way easy even with the many roadwork diversions and would pass by others at the side of the road battling with a big wet soggy map to find their way. We did also pack a map as back-up or to look at a vaster area on a larger scale, however we are happy to say it return dry and not soggy. 

I think once you have used a sat nav on a big trip which gets you to destinations easy, gets you out of a diversion and back on route, helps you navigate/find food and petrol, you wonder what you did before the United States military released the technology for GPS!