"Prime" is relative – the Baltic sea is rather cold and the only reason I sometimes go there is because it's just about two hours and 30 Euros away. When I have more than a weekend, a flight to the Mediterranean is preferred. Plus this is on a island and that'd be another hour or so (ferry or detour).

Berlin is probably the only city for which it's a somewhat attractive destination, but I don't see the rich people here going for it. Flying to italy take only a bit longer, or, if it needs to be close, there are quite a few opulent estates from the 16th to early-20th century within an hour of the city center, quite often with direct access to one of the many lakes.

Well, this is the Baltic Sea we're talking about. The average European tourist wanting sea and sun prefers the Mediterranean (i.e. Spain, Greece, Italy, Cyprus, Turkey, ..) -- considerably warmer, plus cheaper/easier to get to for most people. For Germans there are plenty of other seaside resorts in the country. (Europe is only crowded in some places: large parts are not at all crowded - or even inhabited...)