You already visited this one, and it has not changed much since, one new "soak-your-buddies-on-a-boat-ride" yet nothing *that* great, why not try 2 small parks, Toverland and his motorbike coaster, not very far from Bobbejaanland, and "pick another one in the area". WBW Germany is big enough to spend 1 day, especially when crowded. (imho)
As said previously, plus you'll start to be tired
A whole day to Klotten might be a lot, there is nothing much in the park but the coaster and the new flume for 2005. DO NOT MISS THIS PARK but 1/2 day is enough. I say Tripsdrill Tripsdrill Tripsdrill ! (check distance between them)
If you can, add a German fair, beleive me Olympia Looping, Eurostar, Alpina Bahn must be seen, just for the "here for one week only" factor.
Last weeks of june generaly mean "schools'out". Beware. A bit sooner would be perfect (may->1st week of june).
www.mappy.com and www.viamichelin.fr
Just a few hours from Heide to Fort Fun, don't know more specificaly, I did the reverse itinary in 2003 and it was fine. Fort Fun is an interesting small park, with flat rides unexpectably pushed to the limit, yet nothing really *that" original. Small but fun park. Almost died in the bobsleid ride !
5 hours is short, especially considering the high quality of the major rides there (River Quest has the longest queue, 1 hour is frequent, Mystery Castle, Winja's -first Force then Fear-, Colorado Adventure -forget BTM-, when 1 of this kind of 1st class ride is in a regular park, we are happy, here, there are 4 of them, some 2nd rate rides could be skipped though: Galaxy -simulator-, the mad house, the feary dark ride) I spend a plain day in there, and I visit the park twice a year.
You said it. "Packed"
holiday inn, try the accord group (www.ibishotel.com)
I have no date as of today, but Dusseldorf might be somewhere around july 15th, 1 week to 10 days, I think Dusseldorf and Oktoberfest @ Munchen are the 2 biggest German fairs. Deinitely not to be missed. There is Anakirmes somewhere in July near the Belgian Border, not too bad, includes Olympia Looping, but 5 cars/train in stead of 7 (Munchen). Difference is noticeable
I don't know much but what I know I told you.
Hope you'll make it !