#1 thing to know is that having a toad will not be an advantage in DC. Parking is horrible there. But the Metro goes essentially everywhere you might want to go, is inexpensive, and mostly hassle free. Those of us who live within a 3 or 4 hour drive to DC use the Metro as much as possible on trips there instead of spending half a day circling around trying to find a parking spot.
In all the 35 years I've lived here, I've never needed advance tickets for anything. But YMMV.
If you are interested in things aeronautical, a toad will get you to the Smithsonian Air & Space Museum out by Dulles airport. That is a great museum to visit, btw, well worth the trip.