I just went for the first time this year. The actual model train show is pretty small compared to the other Greenberg shows in the area. Not too many vendors or layouts, but that is likely due to the limited space — the vendors set up on the turntable inside the roundhouse. I’d go just to see the B&O roundhouse and the locos and rolling stock on display. The roundhouse has an impressive display of 19th century steam. I don’t think I would make a trip back there just for the annual model train show.
The Great Scale Train Shows held at the Timonium Fair Grounds just outside of Baltimore are definitely the train shows to attend in the DC-Baltimore. My son and I went in February and we’ll be heading back for the April show. Best train show I’ve been to since attending Trainfest in Milwaukee, WI as a kid.