Trains, other than a visit to the museum, hold little interest for me, save for the odd photo of people doing silly things on them.
The railway museum is worth a visit, even for non anoraks.
I spend about 4 hours in the NRM each time I'm in York. Also the Castle Museum - love the Victorian Street. At The Minster, a half hour or so watching the stonemasons and then a visit to The Orb inside to see the latest progress on the stained glass.
Out of York, Yorkshire Air Museum to step back into the World War II era. Also, if time permits. Ripon for a full day at Fountains Abbey. I'll be up there for two weeks later this year - staying in Ripon and doing day trips to Coldstones Cut, Thirsk, Skipton, Richmond Castle, Middleham Castle and a few more. Bus service out of Ripon is very good and lodgings are about 1/3 to 1/2 the price you pay in York.