As for Germany, German nationality law allows dual nationality under certain, well defined circumstances; for example, a German citizen is allowed to retain his German citizenship if he or she takes out the citizenship of another EU member state (if the that member state's nationality law allows that); another example, if a child is born to a German parent in a country which automatically confers its citizenship to any baby born on its territory ( USA, Canada).
As for Paul Hogan, the issue vis-a-vis Australia was his fiscal domicile when at that time. Apparently he was ill advised by his accountants. He could take out US citizenship, but taxation-wise that would put him in a worse situation as the USA taxes on the basis of citizenship regardless of fiscal domicile. No wonder many USers seek a second passport for expatriation purposes. Countries such ad Dominica and St. Kitts offer economic citizenship programmes for money or real-estate investment, but ex-patriation in the USA is a ten years process which requires you to pay taxes ten years after ex-patriation. Australians don't have that issue.
And yes, it is impractical even to cotemplate obtaining the citizenship of Monaco or Liechtenstein or any other micro-nation for tax purposes. unless your name is Mr.Gates or Mr. Abramovich :-)!
Most of the dual national that I know are either Australian, New-Zealanders, or Canadians who hold British, Irish, Italian, or Greek passports ( very few Maltese, Cypriot an Serbian) Evey fifth Australian is a dual national!
