If you're in Ely during the weekend of July 7th/8th, you'll be right close to Duxford and that weekend is the Flying Legends air show, one of the best warbird shows anywhere. The P-38 'Glacier Girl' is currently en-route from California to display there.
http://www.fighter-collection.com for more info.
Norwich is a lovely city, it has great shopping and a lot of the shops are in smaller alleyways. Find your way through these up the hill to the castle. Or stay in the shopping area and find some cool modern architecture in the Forum, which is the city library amongst other things.
Cambridge is good for the colleges as others have noted. The place is populated by more foreigners than natives during the summer, it will be very busy.
If you look on the
news at the moment, you will see that a lot of the central and northern parts of England have been subject to severe flooding this week. (not just Texas!) so if you're planning on heading to those parts, they may or may not have cleared up by then, and trains could well be disrupted. I'd hazard that Norwich would be better than Lincoln in regards of this but things might have improved by then.
Lincoln is meant to be lovely, I've not been but always meant to go.
You might consider a train ride straight up north of Ely to Kings Lynn, it's on the coast and is generally pleasant. Or a day out in Bury St Edmunds, my old home town, is always nice - it has old ruins of one of the largest abbeys in medieval England and the current cathedral is very nice, with a tower spire completed only two years ago on a 14-th century building. In fact most of the town centre grid is 14th C with some parts dating back to the 11th C so if old architecture's your thing, there's plenty there.
Here's a rail map of the UK which will show you where you can get to.
Hope this helps!
Jo