"We are planning on using Munich for a base this trip... we plan on going to Nurnberg, Regensburg, Rothenberg, Fussen, Dresden and maybe Berlin.... When I add all the train tickets up, it seems it may be cheaper to buy a 10 day pass with unlimited use."
You intend to take day trips from Munich for these journeys? First of all, have you checked some of the travel times involved? A round trip to Dresden takes 13 hours! Even to Rothenburg, you are looking at 5-6 hours on the train. Investing 9-10 hours in a day trip to Prague from Munich just to walk around there for an hour or two seems a huge misappropriation of resources.
If you definitely want to visit the places you named, there is no single base that will make day trips doable. Your best option would probably be a base in Munich (for Füssen), a base in Nuremberg (closer to Regensburg than Munich is, also for a day trip Rothenburg), and THEN to travel from Nuremberg to Prague (about 3.5 hours from Nuremberg), Dresden, and Berlin for 3 separate stays in those places. If you do it like this, it is possible (but very doubtful) that a railpass may be helpful. You will probably do better with the other options that are out there.
Then again, if you are sure you want to base yourselves in Munich for 13 days, there is no problem at all filling your 13 days with day trips to interesting destinations. Salzburg, Nuremberg and Regensburg are all feasible day trips from Munich. You can't really day trip to Rothenburg that easily, but there'd be no problem getting to several other Romantic Road towns, to Salzburg, to Garmisch-Partenkirchen, to Mittenwald, to Landshut, to Dachau, to Neuburg on the Danube, and more. And you could hit all these places using a Bayern Ticket - just buy them as you go, and you can make up your travel plans day by day. Nothing inflexible about the Bayern Ticket!
Do yourselves a favor and don't buy a multi-day pass until your itinerary options have been worked out satisfactorily - this is the only way to know if a pass is worth having.
