Yeah, don't be creeped out by grown men and women in blackface. The Sinterkinds definitely will jar you when you first see them.
I spent more time outside of Amsterdam than in it while I was there. I think it would be worth the day trip to check out Leiden or one of the other surrounding, more traditional Dutch cities. My group spent the day walking around Leiden during its market day (Wednesday) and really enjoyed it. We got to try a lot of different Dutch treats walking around the market and just walking around enjoying the city. The Windmill museum was also pretty cool. I think a side trip like that would be worth it. Also, eat as many Stroopwaffeln for me as possible.
Whatever you do, don't waste your time on Amsterdam's "Christmas Markets." The Dutch don't really do Christmas Markets like the Germans do and the ones in the city are very poor attempts to get you to spend money on street food.
Berlin is a great town. The obvious would be to climb to the top of the Bundestag for the best view of the city. Also, the Bandenburg Gate is right there. Unter Dem Linden Strasse runs from the Brandenburg gate to Alexander Platz and is where you will find all the big museums and state buildings, like the National Opera, Cathedral, etc. Its the closest thing the Germans have to the Mall in DC and worth the walk. I also enjoyed the Checkpoint Charlie Museum, even though it can be a bit cheesy. Berlin is not the prettiest of cities but it has a great vibe to it. The nightlife is great as well, but it doesn't really get kicked off until midnight. Christmas Markets in Germany are awesome, so walk through one if you see it.
Have fun!