A giant leap forward! FoSCL committee member Rod Metcalfe recently discovered the Realtime Trains web site, http://www.realtimetrains.co.uk/search/advanced .
Mark Rand has had a good look at this and it seems to answer all our prayers: for any given day you can see exactly which trains are pathed and which are running and at what times. We can see at a glance how much freight there is, with origins and destinations. Hopefully it will also show up diversions and steam charters, though that's yet to be put to the test.
Try it for yourself!