Speaking as one of the 'larger' passengers... (I generally fly economy, as I mainly fly LHR-JFK which isn't that long):
I don't find Virgin Economy particularly cramped, and don't remember BA WT being any better. In fact I had an absolutely awful experience all round on BA, mainly due to them cramming in far too many flights. 2 flights in same gate at JFK, 1h10 queue to check in at LHR.
The armrests come up in Economy, which helps. I do sometimes miss the 747 3-4-3 arrangement: my husband and I would book 2 of the 3, and the last seat would be one of the last to be picked so we had an excellent chance of getting it to ourselves.
I suppose I don't have high expectations of economy class flights: I'm used to US internal flights.

I'm impressed enough by the fact they feed you. Twice!
On the other hand, my last flight in PE was distinctly unpleasant. You can have those new seats with the bigger tray tables: if you're larger, or pregnant, you can't use the table at all. It rests on an angle on your stomach. Because the armrests are unmoveable, I felt nearly as cramped as I do in Economy.
I'm willing to pay for extras, but add me to the list of people who don't think PE is sufficient to warrant double the price.