Had an exchange with Cal. She noted that the Fairgrounds that the weather is still supposed to be cold tomorrow, and the fairgrounds does not have much seating capacity.
I'm inclined to keep things as originally proposed. CCSP. Like I said in the OP, it is not that tough to get to. If you are not coming from Capital Hill or the Branch Ave side of the Green Line, it is probably easier than the ballpark. Also parking may be easier.
Both the Park and Crystal are 3 stops from L'Enfant, while the Orange line folks can switch at Rosslyn and skip the city. At CC metro, go to the street, head under Rte 1 towards the Sheraton, take a left, and less than a half mile walk down Eads. Take a right, halfway up the block.
As for car people, GW Parkway, 66, 395 opposite the traffic all work well, and Route 1 from the south is pretty direct. Key landmarks if you are on Rt 1 would be the Exxon station at the corner of 23d. Turn South (right if you are coming from the Pentagon, left if you are coming from Alexandria), drive past CC Restaurant and the 7 -11, cross Eads, and the Pub is halfway up the next block.