The Baltic coast is Germanys most popular summer destination, and not just because of the beaches. The area offers medieval cities, many of them World Heritage Sites, posh 19th century seaside resorts, romantic fishermens villages, fairytale castles, nostalgic steam trains, mighty churches etc..
If you decide to stay on the coast... there is a tour company with rave reviews called "Friends of Dave", who offer the "Mega Mecklenburg Tour", which is the perfect intruduction to this region. You see a medieval city (World Heritage Site), a typical seaside resort, a fairytale castle just like Neuschwanstein, you get a typical German dinner in a medieval monastery, and Kaffee und Kuchen (coffee and cake). Instead of wasting six+ hours on the road you actually EXPERIENCE something.
Read the reviews here:
Friends of Dave
And here is Tripadvisors Warnemünde forum:
Warnemünde forum
As you probably notice, most people there recommend NOT tot take the trip to Berlin.