If one steam train would be enough you could try Swanage,Dorset.There is a train that runs from Swanage to Corfe Castle,lovely scenic route.
Swanage is near the beginning of the Jurassic Coast,which is a world Heritage site.It is also within easy travelling distance of Bournemouth and Poole and the New Forest is not too far away for a day out.
I'm not sure that I could stand 30 years of holidays based on steam trains though,perhaps you could celebrate separately?lol
Hope you enjoy wherever you go.
Decx