What you really should do is "Hackesche Höfe" in Berlin - nice little shops, a good cinema and lots of cultural events. Also very special: go and see the Reichstag - but not at daytime, will be far to long to wait till you get in, but at about 9 or 10 pm it's lovely - and you can save the money to have the view from the TV tower.
In Dresden you must see the Art galleries - probably the "Neue Meister" ist more interesting. And if you have time to make a boat trip down the Elbe to Pilnitz - it's a lovely big graden there and an old residence.
Hope you have fun - and message me if you need any more tips ;-)